Have you ever lost so badly that it made you question the future?
Usually a loss is a loss. "That was bad, but we'll get 'em next time fellas!" or some other permutation of dusting yourself off and trying harder next time is generally the most healthy way to handle defeat. You get better and try harder, and there's the belief that the next time you face a similar obstacle you can overcome it.
Sometimes though, you face a setback so painfully complete, so incredibly obvious, that you start to question what the hell you're doing at every fundamental level.