A Tragic Mistake is the event where a hero is given a clear choice, but because they choose poorly, it results the disastrous event that brought the huge impact on their life that made them more miserable than ever. The said mistake may caused by the said hero's own flaws, but sometimes fate also pressed them to chooses poorly as well. While the hero and/or their allies may not realizing the consequence of their wrong choice, that moment is crucial to the beginning of unfortunate event that ranges from merely the hero's tragic downfall to the chain of disastrous events.
The results of this bad choice lead inexorably towards the hero's catastrophic end - had the hero chosen correctly at this point, the catastrophe could have been averted. The said mistake also the crucial part of their story.