Martingale does not always "Win" given unlimited capital. Given unlimited capital it reverts to 1 on a 50/50 spread. With this being said the second you pay a spread, you are screwing the spread towards the dealer, sometimes more considerably than others.

In order for a martingale system to work, besides the proper management and risk controls, you need to have an edge or you will just be working back to 1. Two ways this can be accomplished is:

1 Superior timing (however, if your able to do that you probably are already winning)

2 Trading only during mean reverting times, however this would be considered a form of an edge. Martingale will work as long as the mean reverts, that is the whole premise of the stacking bets, however the quest to predict when a market will revert to a mean and when it is trending is a daunting task in itself.

It's been said in this thread, but I'll say it again, Martingale works perfectly... until it doesn't.