Perhaps it is in the nature of people to attribute the causes of their failures to external factors. On the other hand, they attribute their successes to their own "powers" and internal factors.

In general, it may not be wrong to make verifications for failures as well as successes, but I believe making fake verifications is more dangerous than failure itself !

It is good to analyze failures as well as successes at least with one's own self. But when coming to conclusions, one should admit -at least to himself- if it was because of him or external factors.

When being honest in self-analysis, one would be able to make more real and accurate improvements for next trials.

It is good to know the real value of one's self and the actual capabilities. Even if it appeared to the analyzer as being low, but this does not cut the road on improvement.

I agree that one should never look down at himself; if he does then he shouldn't expect others to give him greater value than he gives to himself. This would always be recovered by hope, and self-motivation.
However, overestimating the self is equally disappointing as well !