A phrase meaning to not let courage outweigh good judgment; is the potentialoutcome worth the risk?
Kid (10 years old): I really wanted to punch that boy for what he said dad, but I thought his parents would probably sue us, so I didn’t.
Dad: Wise decision, son. Discretion is the better part of valor. I’m proud of you. What’d the kid say that made you so mad?
Kid: He said mom was a whore.
Dad: What?!... Why didn’t you beat the shit outta that kid!!
That immense amount of power conferred upon one without commensurate knowledge, experience, or understanding, such that, in effect, the village idiot ends up holding the keys to the U.S. nuclear arsenal, or worse, won't let you into your own office building so you can finish working on that one document that will define the rest of your career and is due tomorrow morning.