you need to set the your targets. dont go with the flow, dont follow the crowd. just make ur profit target and right after the exist dont even bother to look at that coin again
I agree the best time to exit the market is when you're target is already hit. Have self discipline and you should know how to control your emotion, though media are playing the big role for the price of the coins you have to consider also the price chart of the coin as it can give you some idea if the coins is over bought or oversold already.