A small mistake can cause everything, that's how gambling works the level of risk needs to be consider and like you said if greed dominates chance of losing everything will follow, most of the time those experienced gamblers do understand how big is the risk that's why they alloctes certain amount of money or portion of their bankroll but those who are not capable of controlling their emotions chances of losing everything is not by far.
Risks have to be managed most effectively, and f we don't calculate the risks, we shouldn't be taking it in the first place, since risks management is an essential aspect of taking the risks at all, just as you rightly said any mistakes can take us back to an unexpected position at the end since some risks are not worth taking if we clearly calculate their level of tendency of producing negative result.