I would say security and volatility. By security, I mean mostly on the user side.  As most people already aware that most hacking and scamming are caused by 3rd party and human error like not using 2FA, deceived by phishing link, exchange security bugs, etc instead of the flaw in the coin itself. Well, there are some cases where the coin/token itself is faulty but it's not much as 3rd party fault.

Cryptocurrency user needs to raise their awareness on security stuff. People from third world country are usually the one who fall for that kind of hacking.