I agree with this since those who are rich have a stable source of income through their businesses. They have steady cash flow that their own money, when played in gambling then loses, has no significant effect on their wealth. They are just there trying to increase their wealth and if they don't achieve it, then they basically doesn't lose that much. Also, I think those rich people have their own stories of success and defeat, and these experiences would be valuable for them to make decisions in regards to their gambling decisions.
A stable source of income will indeed be a support in everything, including gambling. Those who are rich not because of gambling at first certainly only put a little money (a lot according to us) into gambling, such as putting around hundreds or even millions of dollars, even though it is only a small part of their wealth.
Losing will not be a problem for them, because the allocation for gambling is already determined.
Rich people usually gamble for fun or at the same time increase their wealth by starting gambling and trying to reach the Jackpot.
It is important that anyone should take care of their psychology, and not be tempted to keep putting money into gambling when they always lose.
It will consume however much money you have, there must be full control of the money that will be used for gambling.