You can win from gambling from long run.Because of the house Edge you will lose if you gamble in the long run.If you gamble through poker or player vs player game you have high chance to win.But if you gamble vs house you will surely lose if you gamble long run.Read more about house edge.
It's not only about house edge though. I think in general, gambling, well playing that is, is not a good way for a long term investment. If you want long time earnings in gambling industry, best thing is to get a capital and put up your own casino or online gambling site, that way you also wouldn't have to worry about house edge