We should not forget that you are not the only one player on the platform, there are other players also. The casino's total profit percentage that pays out to all active players. And that's where it mostly depends on how lucky you are and whether you placed your bet at the right time.
This thing you said has absolutely nothing to do with a gambler being lucky and winning in a game of chance or being unlucky and losing.
It is already a known fact that when it comes to game of chance, losing is more guaranteed in the long term than winning, you can gamble and win a million dollars today and be in massive profit, but as long as you keep gambling, you will end up losing all of this money in the course of the months or years depending on how responsible or irresponsible you Gamble.
This is one good reason why knowledge on bankroll management is highly needed. Although it is debatable whether a gambler will lose in the long run I am incline to believing it because of the house edge. Witht he house edge, chance game with 50-50 chance will become 51-49 chance in favor of the casino. That 2% gap is huge enough to make a tremendous impact on the bankroll and on chance of winning in the long run.
This is why myself always treat game of chance as game of fun where I do not play them and anticipate to make profit, but I play simply to have fun and that's it, when ever I want to gamble to make profit, I go for sports betting where I have some level of control even though chance still has its way as well.
For me, no matter the reason, whether it be for fun or profit, one must never forget to gamble responsibly, so yeah, you are right to have self-control.