The sign of a bad gambler is the belief that they are on a winning streak, that luck is just going their way.
Gambling is math and luck. If you can afford to keep doubling, you will win. And as long as you stop after you win, you can never lose. That is why casinos have table minimums and maximums, to prevent winning.
But humans have a well-documented tendency to see instead winning and losing streaks in situations that, in fact, are random. Psychologists disagree about whether this "hot-hand bias" is a cultural artifact picked up in childhood or a predisposition deeply ingrained in the structure of our cognitive architecture.