Honestly, no matter the quality of the preaching, or the clarity of the examples, every gambler learn better having experienced some really big hurdles, those that perfectly understand gambling in moderation are the guys that have either been addicts like myself, or lost considerable amount that got them disadvantaged that they felt the pain and had a swift turnaround and became a disciplined gambler.

No matter how you advise him not to gamble with his last cash, he might be thinking you're against his progress until he does it and loses, then he will fully understand the length of the irrationality associated with his careless decision, as you rightly said, when he's exhausted his funds and he's possibly trekking home hopefully under the hot sun, he'll really understand how foolish he has been and will make a resolution to act more modestly next time.