It's all about self-control and money management IMO, and with that, you can be safe from doing other "stupid" things as well. Even with trading or investing, these two things are still crucial.
Anyway, I learned it from my uncle. He should've been one of the richest guys in the town, but his gambling problem turned him into just an average guy. Imagine what will happen to average Joes? Yep, debt and forever poor.
If you are the type of gambler that learnt from other people's mistakes then you are lucky because this isn't something that a lot of gamblers can relate to, some gamblers had to learn the hard way but I feel like those lessons won't be valuable if they don't experience it themselves. Just like you said, self discipline is key and without it gamblers would easily fall into doing a lot of stupid things