I once tried to write a joke.  Not a "what's the deal with airline food" joke, but a "two guys walk into a bar" type joke.  The former is the true art form.  Stand up requires thinking of something funny, then trying different phrasing and iterations to get the precise wording of the joke.  The comedian then has to make choices around timing, delivery, pauses, attitude, mannerisms and a plethora of other details before it's complete.  As Jerry Seinfeld points out, memorizing the words is step one of a hundred steps to make a joke work.