What is it that makes certain pieces of music, certain dramas, not only have an immediate impact on an audience, but stick with people to become classics?

It could be that a certain tune is enough to make you remember an opera or symphony, a certain dramatic instance alerts the Broca’s area of your brain (that area that craves surprises and thus remembers what’s different) that makes you recommend a play or movie.

In my own entirely unscientific study of what connects with us, I’ve put together a checklist (feel free to disagree).

• For a movie comedy to be a hit (and to be considered funny), it needs at least three big laughs. It doesn’t matter if the rest of the movie trades in tickles. If it’s got those boffo payoffs, it’s successful.

Think of the 1998 film There’s Something About Mary. Lots of chuckles, but three huge laughs: the painful zipper moment, the awkward hair gel moment, the lovelorn tripping cripple moment. The result: $369 million in worldwide sales and, in the consideration of many students of film comedies (albeit those with short memories) one of the top five funniest films ever.

• For a ghost movie to be considered scary or a horror movie horrifying, it needs no fewer than two big scare moments or one scare and one shocking reveal (audiences for these films are less demanding and more willing to accept a suspenseful mood overall).

Think of 1999’s The Sixth Sense. It has a meditative and unquiet mood, but a couple of big audience-gasping moments. One occurs where spirits walk unseen in a hallway behind a room where the characters played by Bruce Willis and Haley Joel Osment are speaking. The other is the big reveal, when we realize the truth of Osment’s character’s line: “I see dead people.” The result: $678 million in worldwide box office.

• A Broadway musical needs perhaps one, but more probably two, big catchy numbers for it to become a hit;

• A romantic drama needs at least one tear-inducing moment (think of Ghost, when Patrick Swayze’s character touches Demi Moore’s toward the end – rivers of tears);

• A thriller needs at least one suspenseful chase or rescue;

• A mystery needs a true surprise as to whodunit.

You might have a long list of examples yourself for these and other genres. In the meantime let’s extend this idea to the classical world.

• An opera needs at least one killer aria (I’m thinking of aria-centric operas, of course, not Wagnerian musical dramas or contemporary works). You’d be right to argue that many operas by Mozart, Verdi and Puccini have more than two great arias, and you’d be right. But they were geniuses. And they knew the value of great tunes at a time when great tunes and great drama were pretty much of a pair.

But even in the sublime Marriage of Figaro with, to name but two amid a wealth of choices, “Porgi, amor” and “Dove sono,” Mozart’s contemporary audience latched onto “Non piú andrai,” which became the 18th-century equivalent of a radio hit, played in cafes and gatherings almost immediately upon the opera’s premiere. It was so familiar to everyone, in fact, that Mozart himself quoted it, quite wittily, in Don Giovanni, aware of the importance of hit tunes in even the most psychologically probing of operas.

I don’t mean to trivialize the dramatic scope of this or other great operas, or even symphonies such as Beethoven’s 5th, with its unforgettable opening, or his 7th, with its astonishing third and fourth movements. But think of works by gifted lesser composers, such as Massenet. Do people really know much more than the “Meditation” from his opera Thais? Or what about Delibes? Would Lakmé be remembered at all if it weren’t for its flower duet, “Dome epais le jasmin”? Would we remember Pachelbel but for his famous canon in D major?

The greatest works are filled with surprises, which is why they’re great, and why we remember them. The not-so-great but nevertheless long-remembered works have just those one or two or maybe three surprising moments. Which is why we remember those moments, but not the whole of the works themselves.

Earlier this month at the Metropolitan Opera Plácido Domingo added a new role to his vast repertoire, the title character in Verdi’s “Simon Boccanegra.” Domingo just turned 69, and made his operatic debut back in 1961, almost 50 years ago. The tenor, now singing this Verdi baritone role, has had one of the longest, most varied singing careers in history.

It’s a rare classical singer who can keep continue to perform leading roles for more than perhaps two decades at the most. It takes a while for the classical voice to settle – often into one’s 30s – but then too quickly the voice ages, tires, and after decades of nurturing and coaxing the singer might decide not to tax what’s left of his instrument.

Sometimes the voice simply gives out. But Domingo, who has been blessed with a particularly strong vocal constitution (among other strengths), is a relative rarity. (Many would argue that one of Domingo’s Three Tenors colleagues, Luciano Pavarotti, kept singing for far too long.) But Domingo’s endurance at the top tier of singers for so many years led me to wonder about the length of the professional career of other singers, both in the classical and pop realms.

Some singers have had remarkable careers cut short by tragedy, of course. Fritz Wunderlich, the great German tenor who specialized in Mozart (but who might have moved on to Wagner) died at the age of 36 in a freak fall from a staircase. Lucia Popp, the Slovak soprano, had an outstanding voice that combined great purity with exceptional passion – she was a fiery Queen of the Night in the famous Otto Klemperer recording of Die Zauberflöte from the early 1960s, and gave a wrenching performance on her record of Strauss’s Four Last Songs. She was concentrating on recitals as her career entered its third decade but she died of bone marrow cancer at the age of 54.

Even Kirsten Flagstad, considered one of the great sopranos of the 20th century, had a career that lasted about 25 years (she died of cancer, too, at the relatively early age of 67 in the early 1960s). She thrived in the 1930s and 1940s, but made several lustrous recordings into the 1950s; these showed some deterioration of her clean unforced vocal line, but no diminution of her expressive power. And she did sing the premiere of Strauss’s Four Last Songs in 1950, in what was considered a masterful performance.

Longevity is a matter of genetics, of course, as well as technique. Opera lovers have long debated the decline in Maria Callas’s voice, tracing it to her weight loss (80 pounds in 1954) or to her decision to sing too early in her career either – flip a coin –the heavier dramatic roles such as Wagner or the lighter bel canto ones. In any event, her voice had declined by the 1960s (some would say the late 1950s), and this sublime artist had perhaps only a decade of prime singing on world stages (but what a decade). She died at the age of 54 of a heart attack.

There are long careers in pop, too. Frank Sinatra sang in public for five decades. Tony Bennett is still going strong, and sounding excellent, at 83. Pop singers have an advantage over opera singers because they rely on microphones rather than having to project to the rafters, over an orchestra, on the strength of diaphragm technique and lung capacity.

You could argue that because Bennett uses a microphone, he’s been able to keep producing a smooth sound longer than the unaccompanied voices of opera singers. But Bennett is still given to letting his unamplified voice ring through a concert hall – part bravado for an octogenarian showman, part thrill at his still being able to let loose.

And pop singers can also count on their dramatic chops to put songs across when their singing abilities diminish. Think of Elaine Stritch, who was never a singer with a beautiful sound (though she did have a strong voice in her day), who now talk-sings, to great effect, during her cabaret appearances. No less a judge of vocal talent than James Levine has caught her recent performances at the Café Carlyle in New York.

Musicianship is musicianship, in whatever sphere. The lucky classical singer such as Plácido Domingo can continue to command an operatic stage into his seventh decade on earth. Some lucky classical singers can move toward the recital hall and extend their careers, as Jessye Norman, among others, has done.

In February, Renee Fleming turns 51, and in August, Deborah Voigt turns 50. These are two of the leading sopranos in the world. And they’re still singing strong. One can never predict how long a singer will last, but these two sopranos have taken care of their voices. Voigt has lost a considerable amount of weight, but has been careful about her technique as she’s slimmed down. One hopes these artists will be around for a long time.

There’s no shortage of singers, of whatever skill. But great singing is rare, and it would be a shame for any fine singing career, popular or classical, to be cut short. We can never have too much vocal music in our lives.

I have left my fair share of new plays and musicals that just weren’t working, and I would probably have left even more if they’d had an intermission (such as Sarah Ruhl’s excruciatingly twee and obvious Eurydice), but I’m still puzzled when people leave opera early.

They know the length going in: It’s generally posted on the opera house website, and most people go to the opera aware that they’ve got at least three, sometimes four and, on rare occasions, five hours to sit through. But toward the end of the evening (and sometimes in the middle of it), you begin to see couples slink out under over of darkness and escape into the night.

I ran into a friend recently just before a performance of Strauss’s Der Rosenkavalier at the Metropolitan Opera in New York. The following day, I asked him if he enjoyed it. He wrote that he did, but that he left after the second act, which surprised me. This man is a seasoned operagoer, and surely must have known he was cheating himself of one of the glories of the opera repertoire by leaving early and missing the sublime trio toward the end of the opera, “Marie Theres'! / Hab' mir's gelobt,” sung by the Marschallin, Octavian and Sophie. But he had a meeting early in the morning.

Then why not just skip the opera altogether? Of course, it has riches in each act, but that final trio is something else.

In a way, it’s like sitting through close to five hours of Die Meistersinger von Nürnberg and deciding it’s not worth your time to make it to “Selig wie die Sonne,” that remarkable quintet in which time seems to stand still as the singers celebrate the good fortune at the composition of a new master song. If you’re already going to devote four and a half hours of your life to this great opera, why not add another ninety minutes and finish what you started?

I realize that people have to get up early for work, and that an opera that begins at 7:30 and ends at midnight is a real commitment. I also realize that many commuters are bound by the tyranny of train schedules, and cannot miss a certain departure otherwise they’d be stuck into the wee hours waiting for the next and cursing their devotion to culture.

I wonder, though, if these folks go into the opera house knowing that they’re going to back out early. Or whether they’ve made a pact with their companion or spouse that they’d go along to the opera, but that they definitely would not sit through the whole thing. Some people are like that about opera. I can understand that. It is an acquired taste (but one that once acquired grows into an insatiable appetite).

Interestingly, few people leave Wagner operas early. Wagnerians are committed to the event, to the length of a Wagner evening (for others they’re like that joke about operas: I sat through three hours of the opera then looked at my watch and saw only 15 minutes had passed). But that’s Wagner for you.

Now, Der Rosenkvalier got me home at a much later time than normal, and I went to bed well past my usual bedtime. I didn’t regret feeling fuzzy the next day, because I still recalled the beauties of the opera, the singing, the experience. After all, one doesn’t attend a performance of Der Rosenkavalier (or Die Meistersinger or Don Carlos or even Don Giovanni) every night. Opera is special, and you make allowances for it, and for the demands that it makes on your otherwise rigid schedule.

It’s not like you can TiVo it and catch the rest later.