When the Pandavas in the course of their wandering are faced with dire thirst, they one by one seek to take the water of a lake, which they discover is being guarded by a Yaksha (sprite). Each one of the younger four brothers refuses to follow the sprite’s condition that the Pandava must answer his questions before partaking of the water and each in turn perishes. The sagacious Yudhishthira does answer the questions (which are an essay in wisdom by themselves) and is rewarded with water and by the revival of his deceased brothers.
A vital insightful answer he provides is to the Yaksha’s question, “Who is man’s worst enemy?”
Yudhishthira’s prompt answer is “His own anger”.