The Downfall

Don't bet when you have negative expectation.

Although the above sentence seems to be such a basic information, one probably need to do some math to fully appreciate the simplicity and precision of the message.

I always tell others, regarding gambling, that you essentially only have two gains in this activity.
One being that you win, you gain greed. You begin to feels like money comes easily, it's a good feeling thinking you could fire your boss soon if this goes on.
Two being you lost, now you want a pay back to what's yours. You gain a mindset to take revenge.

Greed and venge can be seen as hooks, and you are the fish. Once you have them, you keep returning to play the game where you have negative expectation while the casino has positive expectation.

You play their game, by their rules, in their house, carefully designed to make money off you.

To put into perspective, below is a table showing the chance and payout of different bet type of American Standard Roulette. Don't worry if it may looks a little complicated, we only need to go through one.

Let's say you bet on black. Chance you win is 18/38 = 47.368% and for each dollar you risk, your potential winning is a dollar. lets say 1 million gamblers came to the casino betting $100 each on black last year, the casino is expected to receive 100m in bets while paying out $200 ($100 bet+$100 winnings), 473,680/1000,000 of the time, which is 94.736m.

By the law of large numbers this casino is expected to make 5.264m off these gamblers, and their final earnings won't be far off.

No matter what game you choose, you are almost always expected to lose. And if they find out that you, in any situation has the positive expectation (Card counting etc..), you will be kicked out of their house, and probably banned.

Betting when you have a negative expectation will be your downfall.