I've been invested since 2011 and the one thing I've learned is in all bubbles a majority of the gains are made at the very end of the cycle. Trying to guess the top is a fools bet as being wrong by a couple weeks can cost you all your gains. Sure Bitcoin eventually fell to as low as 3k but even getting the top right by within a 12 day window is near impossible.
Don't treat investments as a get rich quick scheme, the true winners are those who diamond hands hold for decades. When it's your time to retire you can spend your coins just like you would dollars you cashed out.
Source and link to Reddit topic: Dec. 4th, 2017 Bitcoin closed a low of $11,502. Dec. 16, 2017 it peaked at a high of 19,660. Being wrong by 12 day would have cost you 50% of your gains. You cannot time the top.