Not only that even if there are a few people that are able to earn money through gambling, for example those that place sport bets professionally, it doesn't really make a lot of sense for those people to teach someone how to do this, after all most likely they found a way to do this by themselves, why are they going to help someone that they do not know and teach them their methods that took them years if not decades to develop? So it is better that people forget about this idea that they have of making money with gambling because it is simply not going to happen.
Case to case and only those who have good skills in sorting out every ideas and information that will help them to gain from this venue of business, we can't generalize as they are people who really made it and able to earn from gambling.
But the number of percentages is not more than 2% the rest of gamblers they are mostly losing from this activities even they've created good system, but due to lack of control and greed instead of winning they all ended up losing to the house.