Mistakes? Hmmm, I have a few to share!
1) Sailing the Great Lakes without a
VHF (and ignoring those 'little' clouds for too long)
2) Towing an inflatable without a cover. It swamped and made a very good sea drogue. We wondered why we were making 2kt downwind in a 20kt blow breeze. Then we looked behind us at the dingy...
3) Not reefing in time. "Oh look, the wind is coming up! We will make good time now." hahaha, that got interesting _fast_.