^ this, but mainly the first thing.
people have to decide whether they want to become a short term (day) trader or if they are investing in bitcoin. for most people it is the latter and as an investment you should never look at short term fluctuations that bitcoin has.
if they make that distinction the point #2 is automatically answered: the goal for a day trader is making profit from fluctuations, so keeping bitcoin when it drops is silly. they should have sold. but for an investor the "goal" is the long term profit due to the long term potential, selling or even thinking about it just because of a short term and small price drop is meaningless.