The problem is that when the course (possibly) will be 2500. You will regret that you didnt sell for 4000 and didnt buy off, thus you could increase the number of your bitcoins by almost two.
After all, those who did not sell at 20, 15, 10, 5 thought similarly that it is not worth selling for cheap, there will be growth soon. They are right, there will be growth, but when will it be?