1. Do not remember electronic wallet password
2. Do not back up your wallet
3. Do not research new services
4. Buy and sell based on feelings
5. Leave your money in the electronic money floor
I cant even imagine someone with lots of Bitcoin in their wallet that is worth a good amount of money saying they forgot the password to their wallet lolXD. Only someone that is very stupid, my money cant go like that Im always careful.
The only mistake I ever made, and that was as a newbie, was not backing up my wallet but I later realized how bad it would be, although nothing bad happened. I dont buy and sell based on feelings, it does happen sometimes but I have learnt to control myself.