I respectfully disagree. Positive balances are the consequence of having "enough luck", not because of a "winner strategy". For each person (doing a martingale) showing a positive balance, there is another (also doing a martingale) with a negative one, and the aggregate balance is negative. Even though you use a martingale approach (or whatever strategy), the expected value of your winnings/losses doesn't change at all.
With a Martingale, the majority of people can have a positive balance. The problem is that the few people who have a negative balance have lost every single cent they were willing to risk. For example, with a typical Martingale system, for every 20 people who have won 100 bitcoins, there's a guy who lost 2700 bitcoins. Your odds of being that guy aren't that high, but if you are, ...
It's like a lottery where you get paid $1 for buying a ticket. But if your ticket gets drawn, they shoot you. Martingale = Hunger Games.