Many people think that bitcoin should move up in a straight line but this is not how the market works. Markets may show us many up and down before moving up and sadly people are not ready for these movements and sell their bitcoin before it reaches the all time high.
Sadly, most people are not patient enough and allow their investment grow, the moment there is a downward slope, they begin to panic and feel it is a time to sell off their BTC. Truth is, if a commodity is straight and on a perfect line, there is bound to be a crash in the long run.