Maybe he got to excited and forget to be realistic, he can't win all the time, that first win of his has entice him to still gamble and try to make more money. What he need is discipline and he needs to learn the bankroll management as even professionals have a losing day.
I think that is because of the tempting of gambling itself that makes his friend playing gambling without stop. We know that it is not good for everybody who plays gambling without stop because we will lose the money in the long run. He gets the lesson from his friend that will useful for him and remind him not to play gambling for making money. It is better to use gambling for entertainment, and in this matter, he already knows that.