Maybe he mean that thing but actually in real situation there's still no gaurantee that we can still earn if we beholf that mindset since it was still a game of chances, actually house edge is the main killer for the gamblers and it will kill the luck of the people if they started to win on those, so as my experience if we are on the gambling scene even if we do some scientific mindset of gambling still the chances for us to win is still on 50/50.
Yeah, what discipline? It can't make you get long term profits. be profitable or loss are depends on how you play, what kind of game you choose, and your luck. Statistically, more people loss than who gets profits, but I know friend here who earn long term profits by doing sports betting.