Having greed is good, its the stupid mistakes that make you lose money. Greed is wanting more money, holding more than you should is not "greed", its a mistake, if you know what you are doing then you would sell at the top and buy at the bottom and make more money aka be greedy.
So all in all, do not make all the mistakes confused with each other, because emotions in trading world is very dangerous and mistaking which emotion is which could be even worse and that's an important thing.
You made mistake because of your greed to hold more and I see no difference. If you want more then that means you're greedy and it's not just a mistake because you're the one who decide to take that risk, hoping to gain. Well, it's a human nature to be greedy, because who don't want to earn more than you should right? But we need to control ourselves and think of the present. If you already earn then take profit already, buy back and hold. It just depends on our strategy on how to take advantage the opportunity for our own benefit.
I believe we can't misunderstand greed with ambition. I think @lienfaye meant ambition by his example, because that is what lead us to seek for more money, for better life quality, for status and every other human needs that for some seem bullshit, but for others are necessary for their personal fulfillment and happiness.
Greed, on the other hand, is the insatiable characteristic some people have inside themselves. In this case nothing is enough for the person. He can have all the money of the world, best life standards and status on his society, but he still want more, even though it's not possible. These people losing all their money trading and gambling due to greed would act in the same manner if they were in a superior position, and some of them were for a while and lost everything for being insatiable!