Being greedy is bad because it can result in different outcomes. For example if you have invest and your investment hits 50% up in your profit then the next thing to do is to sell it now for profits but eventually you will only hold it and wait for it to make 100% and as a result the price dump and the worst part is you won't profit and will lead you to a negative profit. I experience this before whenever i do day trading. I always wait for more then always ends up not to profit. Now i change a lot because i always see that scenario in the past.