I have shared with the community before how I stopped gambling and am currently healing from that addiction. However, recently I had an interesting experience with a friend who was just getting started with sports betting (football). He placed small bets on several football matches, and to his excitement he won 10 out of 11 in a combined bet. He was excited and waiting the final match, knowing it would bring him a huge gain. I supported him telling him he would win and he even promised to give me 10% of his earnings if he won that combined bet with around @1400 odds in total.
The match ended with a win and we were both happy. Personally, I wasn't concerned about receiving any money from him as I was more focused on my recovery to not set a bet or deposit ever again. However, the next day my friend avoided me and didn't follow through on his promise even though I wouldn’t have minded if he didn’t.
What I took away from this experience is how the mentality of gamblers can change after a win. The thrill of success often leaves us wanting more and in this case it seemed like my friend was caught in that cycle, as I was feeling before too and he was unable to honor his word probably because he wanted to keep increasing his gains and bet more. It's a reminder that the brain is never truly satisfied when gambling, there's always the desire for more. I believe that friend deserves an advice, but I don’t want to embarrass him myself, is there a good way to talk to him without making him feel that Im indirectly asking him for the money he promised me?
There is a possibility that your friend is rethinking about the winnings he got should not be given to you, because all the capital to bet on the match was entirely from his own money. What you said is right, people will never feel satisfied when they win a game from gambling, they will try again to bet on the next match without your knowledge rather than having to give it to you.
Perhaps when his friend won, he realized that the 10% he told OP was still a big amount, and it seemed like he regretted the amount he had to give,
though he was under no obligation to do so because it was still his choice from what I can see.
Now, if he were to enforce the word of honor, he wouldn't ignore the word he had given, even though the truth is that OP didn't really expect the winner to do that because he just supported his friend, so it wasn't a big deal to him whether he kept it or not.