When I plan to gamble, I usually aim to spend around 15% of my income on deposits at gambling sites. I play casually and with small bets. If I win, it will be something good, but sometimes I lose quickly, making me angry and emotional so I deposit again, and again. Until my money was almost gone, the conditions were very bad. I don't do that often, but I have done it once or twice.
You need to be careful because it's a sign to be a gambling addict if you deposit more money and you angry after you lose all of your money. Try to learn if gambling isn't for making money, if you think 15% of your income is big for you, you can reduce it to 5% or lower. In case you lose, it will not hurt you.
Remember, curing a gambling addict is really hard, prevention is better.