Experts treat gambling as a source of income, so they bet on themselves because they’re confident in what they’re doing and believe they can be profitable. These are the ones who raise a realistic bankroll and set realistic targets. let's say on average, if their funds grow by 10% in a month, they’re already happy because over time, it compounds.
Ordinarily, people tend to recommend that you make 10% in savings from your monthly income and should you be earning 10% from your gambling bankroll, I think it’s to the same effect or result which is a good one. For some, it might depend on what your bankroll is but, that’s still positive you know and in a way, you stay profiting. It however shouldn’t motivate you to wish to have a larger bankroll as this is still gambling and loosing can some with such ease that would be regrettable thereafter.
10% is actually more than letting your money earn interest from a bank. Most of the time you can only earn less than 1% annually from your bank deposits. So if you can guarantee 10% earnings from your gambling activities monthly, that would be great. However, this is gambling, so don't expect that you will truly earn 10% from your games every month. The more likely will happen is losing 10% of your funds from gambling.
So I don't think anyone on their right mind will guarantee you 10% profit of your bankroll on a monthly basis. Otherwise, he is giving you false promises and can easily ruin your finances. This is gambling, you should know the drill on this game.