Your own stupid idea
I was recently listening to a podcast about the Branch Davidian cult, led by David Koresh, and how the FBI attempted to end the standoff by, among other things, flooding bedrooms with light to prevent sleep and blaring the screams of dying rabbits over loudspeakers to drive the Branch Davidians insane and hasten their surrender. Apparently, someone thought this was a good idea, and apparently, no one was brave enough to tell that person they were wrong.
The lesson? Speak up. Trust yourself. If you don't pursue your own stupid idea, you'll end up pursuing someone else's stupid idea, and the latter will often be much, much worse.