My dad was a compulsive gambler, he kept his secret until we found out he was $35k in debt. It's the only addiction where you can pretend you're doing a good thing, he said he was trying to "build a better life" for us. He thought he had a system for playing video poker...

Ironically I worked briefly at a slot machine company years after and discovered that casinos constantly move machines around on the floor. Even if you think you've found a hot machine, it's soon replaced by an identical one. By law they have to put machine numbers on the front, but good luck wandering the floor trying to find your lucky machine again.

Its the only addiction where you can lose everything in one night.