The most common mistake would be panic selling and weak hands, honestly.
If you invest in bitcoin then you are probably going to have to prepare for the long term. Trading bitcoin short term will mess up your entire trading psychology because you'll keep on trying to go for just that little more profits.
If you are trading bitcoin short term, make sure that you have a stop loss level in mind, and a target where you sell your coins. Otherwise, you'll always fall into the hole of selling low and buying high.
Indeed you explained quite well, the high expectations of beginners or inexperienced traders in a short period of time is the reason why they go for the panic selling during a dip. You should need to keep your calm in long term trading.