First one I sold was one that I screwed up and re-did several things to fix. Thought it was the fugliest knife ever made and intended to test it to failure to check my heat treat, but some guy at work saw it and said how much for this? I told him what I thought of the thing and he ended up giving me $50 bucks for it anyway

Of course, he got about 60 hours of my work for pretty cheap. Unfortunately, half of that work was correcting mistakes made while correcting mistakes, while correcting...
I have the king daddy of all mistakes to tell ya. I was preparing to heat treat my first (and so far only) 440C knife. Took my time setting the HT oven and double-checking the HT specs from Admiral Steels and when I got done realized I'd forgotten to drill the #@$#@ holes for the pins

That's not the end of it... I endeavored to try annealing the tang with a blow torch and tried drilling - no joy. The damn stuff air hardens too! Right now I'm planning to get some carbide bits from Tracy's outfit and finally get the thing done. I really think it would be cool to have a thread dedicated to the mistakes that we all make. That way my post count could rise exponentially
Regards,
Dave