now a lot of investors are investing in bitcoin, therefore bitcoin has increased very rapidly, if bitcoin decreased what should be done?, whether the investors will lose? 
If you're into long time investment and wants to gain profit in bitcoin withdrawing it when it decreases a bit is not advisable. Considering that some says that bitcoin value will rise this coming years leaving it in you btc wallet is probably a good choice only if you still have extra money outside to use if you have something to buy and just let you fund in btc gain interest as time goes by.