I agree but partly! There are situations when people are really greedy, the Russians have even such a proverb "greed of a fraer ruined", in this proverb there is a share of truth. However, there are situations when not greed seized man, namely, HODL.
It is the human nature that they want everything some extra, and such character make them greedy. I think that some investors get noting only because they are hopping to get more and more, they never compromise on what they have or what they got. Such character always causes a big lost for them.