Of course, if you play roulette or dice, it all depends on luck. But if you play poker or bet on sporting events, then a lot will depend on your skill. And the higher your skill, the more likely you are to win.
Even your are right that if a person have good skill on analysis of sports and as well you also mention games like poker may be they are winning probability can be increased but if you look at the ultimate result then it is also depends on luck.
Like no matter how much you skill on your Sports analysis you can also lose bet like we see on many matches that is stronger team lose against a weak team. And also in poker it is also depend on what types of card you are getting.
The truth is that, there are lucky based games and there are also skill based games in gambling. The skill based games are those ones that doesn't really depend so much on luck but more on the gambler's skills and experience in gambling.
But when it comes to luck based games, even the most experienced player can lose countless times. It's just as you've rightly said, using sports betting as an example, where even the strongest teams can potentially lose its form and starts losing. This shows just how unpredictable gambling can be, and this is the more reason it's advisable to always approach with extreme caution.