No matter he emphasis on Self-control, there are still player who would never obey the rule because of greed and then they would come back to pour their frustration on casino sites after making loses.
That's true as not all of the gamblers are responsible, you can call yourself only a responsible gambler if you know your limit.
Control is important as you are controlling the risk here.
Like you mentioned been content with little winnings, many will never be content, since gambling is their only source of income and this is really wrong.
This is not a good mentality, gambling cannot be source of income if you don't have the talent or the skills to do it, but one is sure, we gamblers will be a source of income of the gambling sites operators.
Gambling is not supposed to be a source of income and if at all you choose to make it a source of income, just learn to avoid greed and there will surely be record of more wins than loses for your games.
Play for fun, that's more matured thinking.
You know if you can consider it as a source of income if you can make consistent income in gambling, but winning just once and declared you are good is you yourself being delusional.