Larry David has never pretended otherwise. George Costanza is Larry David. Not approximately, not as a loose inspiration — specifically, precisely, detail by detail. The plots that happened to George Costanza happened to Larry David. The failures that define George's life were Larry David's failures, examined under a comic lens so strong that they became something extraordinary.
Larry David co-created Seinfeld and served as showrunner until the end of Season 7. In that time, he drew from his own life with a directness that most autobiographical artists do not attempt.
The unemployment benefit scheme was a real thing David did. The contest was a real contest between David and his friends. The incident in which George quits his job impulsively and then tries to act like it never happened was drawn from a specific day in David's professional history.
The joke was always that the specificity of the detail was the comedy. The more precisely David described his own humiliations, the funnier they became.
One of the show's most famous George plots — quitting his job in a rage and then trying to simply return the next day as if nothing had happened — was based directly on something Larry David did as a writer for Saturday Night Live. He quit, went home, reconsidered, and returned the next day to find that no one was going to acknowledge what had happened. The combination of momentary courage and permanent cowardice is so precisely observed because it was precisely experienced.
The Contest is based on a real contest that Larry David had with his friends. He won. He has said this in interviews. The achievement was taking something real and deeply private and finding the exact way to put it on national television without naming it directly. The circumlocution — 'master of my domain,' 'still in the running' — came from the same comic instinct that produced the real contest.
When Larry David created Curb Your Enthusiasm for HBO in 2000, he removed the fictional frame entirely. Where Seinfeld presented his experiences through George Costanza, Curb presented them through Larry David playing himself. Curb Your Enthusiasm is Seinfeld with the disguise removed. It confirms what the show had always implied: the failure, the awkwardness, and the social catastrophe were not invented. They were lived.
Larry David's failures — the quittings, the contests, the schemes that backfired, the social disasters — produced the greatest sitcom in television history. The lesson, if there is one, is that the most ordinary embarrassments, examined with sufficient honesty and sufficient craft, become extraordinary comedy. David did not need exotic experiences. He needed to look at what had actually happened to him, and find the exact words to make it funny to everyone else. That is the hardest thing in comedy. He did it for nine seasons and then kept doing it.