Every good sitcom depends on its characters and their chemistry - storylines can only take it so far.
For that very reason, Friends has gone down as arguably the greatest sitcom of all time, with many similar and some even accused of pretty much outright copying it. The characters on the show are what have made it endure in popularity and made it so eminently quotable.
The key to the show is that each of the characters has their own individuality that compliments and engages their surrounding cast. Joey, Ross and Chandler are the prime example of this, they are all beloved for different reasons, and all are relatable in their own way. And each character transitions fluidly in a regular rotation between main protagonist and supporting cast as the story requires.
Basically, Joey, Ross and Chandler all contribute equally effectively to the show whether the focus is on them or not. But can you tell which one of these said the following quotes?