[AaronBrown]

While I see the points in both (actually all three) sides presented here, I think about it a little differently.

It's extremely hard to know when you are playing your best Poker. You don't have a coach or partner to critique you. While it can't make sense to quit every time you lose a few pots, it does make sense to worry if you "never fail" to lose back your profits. If you track your results and discover that you have real losing streaks, beyond what is expected by random chance, it certainly makes sense to try to correct that. Quitting is only a short-term patch, you need a better long-term solution. But until you figure one out, better not to play.

However, the best reason not to quit after a loss is the loss should increase your future expected value. If you went to showdown and lost with a strong hand, you can expect people to fold faster against you. If you got called with a complete bluff, you can expect people to call your future bets. If you folded after contributing a lot to the pot, you can expect people to bluff you. You can exploit any one of these tendencies.

The biggest reason for losing streaks, in my experience, is playing the way people expect losers to play. That means each loss makes you easier to beat. Doing the opposite makes your losses productive.

If your losses are not productive it's either because you're not losing the right way, or you're not adjusting your play properly afterwards.