I agree with you that there is no guarantee in gambling, because it will only depend on luck. The problem is we never know when we will get such great luck, so all we do is try and try to be able to get lucky and succeed in getting a very big win.
I also don't know what the definition of a professional player is, are they those who never stop playing? do they know when they will get lucky? (and honestly I'm not sure about that), or those who have continuous luck? also I'm not sure there are people who continuously get great luck.
When you gamble for a long time and can predict the ratio of win and loss which will be very accurate then you will consider yourself an experienced gambler. Although no one can claim to be an expert in gambling because luck plays the most role here. However, our emotions often make us think of ourselves as experts. This is only the effect of our emotions and greed.
Since it is not possible to guarantee who will win and who will lose in gambling, many people make predictions and increase or decrease the amount of their bets, and if they are lucky enough to bet on a large amount, they get a very large return. And then they start thinking that they are very clever. This is always seen among gamblers.
Ah yes I can understand if it is like that, but the problem is whether anyone can predict accurately. Maybe it will apply when we are in sports betting, but if it is a slot game, then who knows or who can predict what the ratio will be like.
Some people look at the RTP to play and they believe that it can give them a greater chance of winning. But according to what I have experienced, RTP does not have much effect and I can even get maximum winnings at that time in a game with an RTP that can be said to be very low.