It is true for casino games - games with random result. In sport betting you can get good result if you good at maths, can search information, make high quality analyze, and can play without emotions 24 hours per day.
I can`t say that it is easy, but strategy, risk management and money management give you an opportunity to get profit regularly.
PS. And you need to have some tricks, to struggle with casino restrictions like bet limits and ban of the account.
I think it is not enough, even to be persistent and devote a lot of time to it, it is important to understand that the strategy that was invented or taken from someone works, and this can only be checked after a long time and many balances. During this time, nothing may remain of our bankroll, and we will no longer have time to check strategies again. Moreover, the casino always monitors that there are no too winning players, they put the cash flow of the institution at risk and the casino will never allow winning players to become more than losing ones. In general, at the moment I am definitely a losing player, because I do not have a strategy, even after a long time spent in the casino.
Opportunity doesn`t means guarantee. Also it can be bad strategy or some mistakes in management. Also, if it would be easy enough, how the casino could get the profit?
I don`t recommend anybody to gamble for profit, i just mark that it is possible for some people if they are good enough for it.