Yes, exactly. Even if you initially intend to hold "long-term", if you don't have
some form of risk management, there is too great a chance your mind will slide from Bitcoin illusioned to Bitcoin desillusioned purely because of a bear market – after all, it was merely a bull market that led you to the other opinion in the first place! – which creates a risk that even if you end up being correct in a few years, you will have sold out near the bottom and forsaken Bitcoin.
The importance of managing your expectations in order to have the ability to execute your plans is incredibly important IMO.
By the way, the flattest long-term support trendline that is being drawn nowadays, even though it is much less steep than the one drawn in 2011, still has the price doubling every couple of months. It would not be too difficult to go below it given enough time.
EDIT: I should add that if you are young and have like $5,000 or $10,000 in bitcoins--just ride this f*&cker. Worry about portfolio diversification in your thirties or after you're up $50k - $100k.
Sure, if the money is nothing to you to begin with or it is easily regained from income, then there is less worry in the first place and you won't have to care.