How has It’s Always Sunny In Philadelphia stayed funny for so long?

A new video from Film Radar has an answer, and it hearkens back to the show’s origins—namely, how it was created and written by the core cast of Rob McElhenney, Charlie Day, and Glenn Howerton. Having the actors be so integral to the creation of their characters has allowed the show to achieve “a level of control and collaboration” that most sitcoms can’t. This has allowed for a remarkable sense of consistency in personality, history, and motivation.

The video also touches on how the show’s structure is, in itself, a subversion of the “self-imposed stasis” that’s central to nearly every sitcom in history. The fact that the core group never changes or intermingles with other social groups is here an extension of their characters rather than a device of the writers and producers.

Of course, all of that might change now that Howerton, who plays Dennis, may be leaving the show. Never before has the show had to deal with such a seismic shift in its central dynamic, so this next season is likely to be a telling one in how the show stumbles into its future.