Not buying Bitcoin when I should've bought it. Not being educated about Bitcoin after I had some units of it. Not selling my Altcoins when I should've sold them always waited for moon which never came then I turned into a bagholder for years now. Lastly blowing my cryptocurrency account with carelessness is my highest regret.
I think we can all sympathize with no buying all the bitcoin that we could when its price was very low, I think many investors tried to compensate for this error by investing all their money in altcoins that were not worth it and paid the price because of it, and the saddest part is that many of those investors never learned anything from it and kept doing the same mistake over and over again not realizing their mistake until their capital was completely gone but at that time it was too late to do anything.