Life is indeterminate and at best a blip.
If the thing he is doing is not providing fulfillment, it's probably not the right thing. I'd advise not to wait. Search for what brings growth and contentment. Go for it.
Having a rich life full of new experiences can be done without chasing the dollar.
This is not meant to be hippie talk. What it really is risk management. When you perceive that you are losing you psychologically want to increase risk to make up for it, leading you to make poor bets. It applies in trading (gambling), where I learned it, but happens in life as well.
Someone in his position needs to consider whether quitting is legitimately a better bet rather than letting emotions dictate.