It depends on your strategy for me I don't wait until 20% for me to take profit, most times, some coins hardly make such gain, but taking profits like 5% or 10% many times could be a good idea, coins normally makes such gain many times before it could go as high as 20%, so I believe in taking profits as soon as you see them and re buy when it dips down again.
greed is indeed dangerous. well, not only in trade, all things related to greed will be easily broken. well, therefore, we must be grateful to avoid the greed that always arises, and damage our strategy.