Seems lots of bitcoin investors did a wrong decision way back dec. 2017 and this is the reality that crypto is very risky and the price of crypto are completely unpredictable and volatile as well.
Investors who are smart sold half of their holding before the dump occurred. However, if you ask me, I don't see crypto as something which risky as you proclaim because of it volatility cause every investment as it own dump in price season and crypto lost can still be recover if the trader/investor is patience.