If that person was someone like Warren Buffet, e.g. with a massive track of success behind them, then why not. 20 per cent of a billion is a lot more than 50 per cent of a million.

But for random nobodies who think high of themselves, hell no.

It makes sense to walk away even in the game theoretic sense. Many people think in terms of prisoner's dilemma, when it is actually iterated prisoner's dilemma.

Its true in a game-theoretic sense, but I'm actually talking about being honest (and rational) with yourself and what you're able to contribute. There's many other factors that have been mentioned by other people here.