The best lesson is often hidden inside the reason something failed.

Failure comes with a specific explanation attached, and the explanation is usually more valuable than the outcome was costly. Something did not hold: an assumption, a preparation, a relationship, a piece of timing. That precise information is not available anywhere else, and it is generally discarded in the rush to move on.

After something fails, before you recover from it, write down what actually went wrong at the level of mechanism rather than mood. Not that you were unlucky or not good enough. What specifically broke. That paragraph is the return on an expensive experience.