Yes you should not be greedy because the market is depending on supply and demand so you will not be always earning profit in the market, invest only a value that you are capable of losing that is the reason you should not be greedy on cryptocurrency.
There are times when you would be lucky being greedy because you can get a higher amount than what you planned but if you experienced it first than losing then there is a tendency for you to become more greedy in the future and someday it will back fire. One will just wait for the price to climb higher and in one instant, the price suddenly drops and instead of being in profit, you are at a loss and it would be a big lesson for you. You should always have a trading plan and stick with it to minimize your losses.