Experienced leaders have made mistakes. The important question is whether the mistakes indicate a character flaw or simply a blunder; a lapse in judgment.
Now the minute that statement is made, critics will rush to claim that the blunder of their opponent was in fact a character defect but any reasonable application of fairness should acknowledge the difference. In our hyper-critical society, leaders are scrutinized for any blemish and there is rarely any acknowledgement that the person who has a few scars may be all the better a decision-maker because of those negative experiences.
Churchill was a better leader because of Gallipoli.
One can argue back and forth about Carly Fiorina's record at H-P and yet it is important to remember that serious leaders come with the problems (and lessons) of their past.
[Some fail to learn and just bring the problems.]
Others, however, bring less experience and thus fewer mistakes. They may be wizards and yet that may also pose the question of whether the big mistakes of their life are lurking in the future.