"Failure is often a better teacher than success, you can succeed all your life by dumb luck and never learn a thing or misattribute the success to the wrong elements." - It certainly sounds reasonable in at least some situations (e.g. failing at losing weight does not teach much), but is it true? Luck is necessary to succeed, since most complex situations or actions have probabilistic outcomes, but I have not seen many people being taught much by failure, and for good reasons. In theory, failure can be a good teacher: one has to analyze the causal relationship between the events that led to failure and with a cool and serene mind make a better plan for tomorrow. No judgement, no regrets, no mortification of mind and flesh. They wake up feeling energized thinking about what they have learned by the previous day's failure and they are even more ready for success than yesterday. But this is not realistic; it is easy and common to feel depressed, useless, and small after failure, energy goes down, not up (of course there are exceptions everywhere) and causal relationships are challenging to unravel (when at all possible) and also may change over time and space. Success, on the hand, means that something worked (at least once!).