Winning is so rare to happen, you are right about that.
This is the big reason why we should be doing withdrawals whenever it happens not the other way around which is being greedy and trying to gain more.
It's better if take advantage of one win per day. If you happen to double your money, take it. It's not like we worked hard for it. A win will always be a win and withdrawing doesn't mean we are weak, in fact, it's the opposite of it.
Some people are so overconfident and that's why they find it difficult to withdraw their winning, they usually believe that they can use the initial winning to make more profit and on the process of doing so, they end up losing everything. Like you said, it's wise to withdraw some winning and only keep a small amount, such practice doesn't make us weak. Sometimes, I even withdraw my cash out offer while the game is still live.
Or maybe they feel that adrenaline that they can continue winning if they push for more, and same with both of you, the principle of cashing out is a wise decision if opportunities happened to you, I mean a sure profits should be taken out from the casino, try to treat yourself and leave, as you don't know what will be your fate the next time you enter and play. Always take that edge when you still have that green positive in your wallet, else, you'll be led by tour greed to lose everything back together with your initial deposit.