I feel he made a huge mistake in keeping a profit because 12 btc is not small amount, I think he has gained about 8 btc and started thinking greedy, so he lost and when he wanted to recover lost funds is too late, bad luck come and defeat increasingly, this is a very valuable experience for better gambling.
It's not about luck. If you gamble you will eventually lose too much. You can't have bad luck and keep losing every time, it's not how it works.
If he made 1000 bets, probably at least 400 were wins, this is how math works, so he probably at some point would end up winning, but it wasn't enough.
If you want to check me test a casino game with free balance or money from a faucet and you'll see that at some point you'll have more than when you started, but none of us wants to leave with a few coins more in our pocket.