I think the problem most of the gamblers when they are winnings is, what is the right amount to stop once winning, usually they didn't notice that they are losing already after winning an amount. It's either they are getting greedier or unable to tell when is the good amount to stop, usually when I notice that I am winning, I will withdraw my 85-90% of all my total money from the site and I will leave the remaining 10-15% to play with, so if that made me earn more, the better but if I ended up losing, then I already managed to secure my profit.
You’re right and not only during take profit is the problem but also during the time on when to quit. Many gambler doesn’t have stop unless their bankroll was totally depleted.
More problem is when they start to deposit again just because they can’t accept those losses and want to recover it back until the losses inflate on insane level.