I have hardly played on virtual because of the high risk involved in it and skin betting is one fast way to lose your money. Your friend started wrongly by playing with $300. He should have started lower to try what he learnt on the streamer display because most times what you see watching them isn't really the outcome when you play. However, he was able to realize his mistake and retrace his step.

Generally, chasing of loses is the quickest way to lose in gambling. So the way to regain your boundary is to come back to the consciousness that you are gambling irresponsiblely.