What do you think has kept The Simpsons going for so long?

It probably wasn't until Labor Pains that it really hit me, the show has been on for 25 seasons! And 3 seasons of 1 minute shorts back in the Ullman days. As a die hard fan I can honestly say that the past 25 years are what I call a pyramid. The writing, voice acting, and animation teams, these are the points of the pyramid that makes The Simpsons the best it can be. That's my opinion though, what do you think?