There is something unusually durable about a good 1990s sitcom.

Decades after their original runs, shows like Friends, Seinfeld, Frasier and The Fresh Prince of Bel-Air are still being watched by people who were not even born when the episodes first aired. Clips circulate online, old jokes become memes, and streaming services have given entire series a second or third life.

Nostalgia explains some of this popularity, but it cannot explain all of it. Younger viewers have no personal memory of waiting a week for a new episode of Friends, yet many still watch the show from beginning to end.

The best ’90s sitcoms have survived because underneath the outdated technology, enormous apartments and very specific fashion choices, they were built around things that have barely changed.

The problems were ordinary and recognizable

Many ’90s sitcoms had remarkably simple premises.

Friends was largely about young adults trying to figure out relationships, careers and friendships. Seinfeld turned tiny everyday frustrations into entire episodes. Frasier followed an intelligent and successful man who could give excellent advice to everyone except himself.

These weren’t complicated concepts.

The comedy came from recognizable human behavior.

People got jealous. Friends misunderstood each other. Dates went badly. Families argued. Coworkers became annoying. Someone said the wrong thing and then spent the rest of the episode making the situation significantly worse while trying to fix it.

Technology changes quickly. Human awkwardness does not.

A joke about an answering machine might require a little explanation for a younger viewer, but the panic of leaving an embarrassing message for someone you like remains perfectly understandable.

Characters had time to become familiar

Traditional network sitcoms often produced more than 20 episodes per season.

That is a huge amount of television compared with many modern streaming comedies, which might produce eight or ten episodes every couple of years.

Long seasons gave sitcom characters room to exist outside major storylines.

Not every episode needed to transform someone’s life. Characters could spend 22 minutes arguing about a parking space, attending a terrible dinner or trying to hide a ridiculous mistake.

Over time, viewers learned tiny details about them.

You knew how Joey would react to food, how George Costanza would respond to embarrassment or how Carlton Banks might behave at a party. The characters became predictable in exactly the way real friends can become predictable.

That familiarity made audiences want to return.

Watching an episode could feel less like starting a story and more like spending time with people you already knew.

The ensemble mattered more than the premise

Many of the strongest ’90s sitcoms were built around groups rather than one central star.

Friends had six characters who could be paired in different combinations. Frasier balanced Frasier, Niles, Martin, Daphne and Roz. Seinfeld became increasingly dependent on the strange chemistry between Jerry, George, Elaine and Kramer.

A strong ensemble created endless possibilities.

One episode could focus on romance. Another could be about work. Another might pair two characters who rarely spent time alone together and discover an entirely new comedic dynamic.

It also meant viewers didn’t need to love every character equally.

Everyone had a favorite.

More importantly, the characters were allowed to be flawed. George was selfish. Ross could be painfully insecure. Frasier was pretentious. Will could be immature.

The shows did not always try to make their characters admirable.

They tried to make them funny.

The jokes had room to breathe

The structure of the traditional sitcom imposed strict limitations.

Episodes had to fit into television schedules. Commercial breaks appeared at predictable moments. Stories usually needed to reach some kind of resolution within roughly half an hour.

Strangely, those limitations often produced incredibly efficient comedy.

Writers had to establish a situation quickly, develop it and deliver a payoff. Multiple storylines frequently collided near the end of an episode.

Shows such as Seinfeld became particularly good at this. Something that appeared to be a meaningless joke early in an episode could suddenly become essential to the ending.

The studio-audience format also influenced timing.

Actors paused for laughter. Reactions were given space. Physical comedy could develop without rapid editing.

Modern comedy often moves faster, but speed is not automatically funnier. Many ’90s sitcoms understood exactly how long to let an uncomfortable moment sit.

They existed before everyone carried a smartphone

One accidental advantage ’90s sitcoms have today is that their worlds feel refreshingly disconnected.

Characters had to show up somewhere to see whether another person was there. Plans could fall apart because someone missed a phone call. People got lost. Information was difficult to verify immediately.

A surprising number of classic sitcom plots would end within 30 seconds if every character had a smartphone.

That limitation created opportunities for misunderstandings, coincidences and unexpected encounters.

It also meant characters spent enormous amounts of time physically together.

The gang on Friends sat in a coffee shop. Jerry’s friends constantly appeared at his apartment. The characters in Cheers, which ended in the early ’90s, gathered in the same bar.

Nobody was sitting silently around a table looking at five different screens.

That gives older sitcoms a social quality that can now feel almost comforting.

They weren’t afraid of standalone episodes

Modern television often encourages viewers to watch every episode in order.

Many ‘90s sitcoms didn’t require that commitment.

You could accidentally catch episode 14 of season five and understand almost everything within minutes. Characters developed and relationships changed, but individual episodes usually told complete stories.

That makes these shows extremely easy to rewatch.

You can choose a favorite episode without remembering exactly what happened before it. You can leave the television running while doing something else and return without being completely lost.

Streaming unexpectedly made this old structure even more useful.

Shows designed for weekly network television turned out to be perfect comfort viewing in an on-demand world.

Nostalgia helps, but good writing does the heavy lifting

Of course, nostalgia is part of the appeal.

The clothes, hairstyles, apartments, landline phones and coffee shops can instantly transport viewers who remember the decade.

But nostalgia has an expiration problem. It cannot make hundreds of bad episodes entertaining.

The sitcoms that survived did so because their comedy was built on strong characters and recognizable relationships.

The technology surrounding those characters became outdated. The situations didn’t.

People are still falling in love with the wrong person, embarrassing themselves at work, competing with siblings, lying to avoid awkward conversations and complaining about their friends.

The ’90s are gone.

Fortunately for sitcom writers, human beings are still ridiculous in almost exactly the same ways.