Actually bitcoin is like others coin so its price can be high and low. So if people see that the price of bitcoin is high so they can sell. They can save something for the future also. There is nothing as stupid decision.
If you buy your bitcoins in higher amount, and then because you feel worry and feel panic because of the successive declining the value of the market in said coins, then you decide to sell it in lesser amount or in cheap amount, you will called stupid of that, because we joined this and invest in bitcoin to earn a profit not to lose our money.