For me, regret not taking a risk and fail to win a life changing amount is more painful.
Because as time goes by we will forget about our losses on gambling, and I'm sure all gamblers also don't want to remember about that.
But the regret of fail to win big money/life changing money will never be forgotten, we will always remember it - that's why it hurts more than losing because of taking a risk.
The same, will consider this as a painful regret, not daring to risk a bet that already knows the victory.
I think if this happened to me then that moment would not be forgotten and always remember the incident where we did not take action on a bet that won a large amount of money that could change the life even more decent or say become rich in the bet just that we did not take the risk.