I received a rather strange question this past week from an inventor.  He wanted to know if doubling down in blackjack is an advantage for the Player or the Casino.  I find it strange because my expectation is that someone trying to invent games would probably understand what creates house advantages and what creates Player advantages.    I don't necessarily expect the average Player to fully understand this, but if you're trying to invent a game, you need to understand what levers to pull in order to make the game's math work out correctly.