if you have unlimited funds, then doubling your bet every loss WILL guarantee profit however you do not have unlimited funds - ultimately what this betting strategy does is give high odds of small payout, and low odds of high loss (i.e. your entire bank). given limited funds (i.e. reality), it is still in the host's favor. example: player has 3.1 million coins and starts betting at 100k, doubling each time he loses. each bet is 60/40 in host's favor. odds of winning with 100k bet - 40%, win 100k odds of winning with 200k bet - 24%, win 100k odds of winning with 400k bet - 14.4%, win 100k odds of winning with 800k bet - 8.64%, win 100k odds of winning with 1,600k bet - 5.18%, win 100k odds of losing with 1,600k bet - 7.78%, lose 3,100k tl;dr: your odds of winning 100k are 92.2%. your odds of losing 3.1M are 7.78%. with these specifications, long term this betting strategy turns out to increase the players odds to about 41:59, but as long as you have finite amount of money it will never be a winning game for the player.