What's your biggest financial failure that you are comfortable to share?

Mine was donating almost 40k to a villager in need over 5 years period only to found later that they use it for alcohol and lottery tickets (lotto or something). After that I gave up. So fucking hard to do personal due diligence. I just don't have the bandwidth to do it. Rm40k without proper due diligence. This was when I was young. I skipped lunch and dinner to help them. Can even be upfront payment,