[gazuz]

This is very similar to the coin flip trick, the theory was studied by Martingale. I found a complex explanation of it here:
Martingale (betting system) - Wikipedia, the free encyclopedia


Simply explained you double your stakes everytime you lose so that the winnings of that second bet covers the losses of the previous trades plus the initial profit we were aiming for in the first trade.

For example:
Buy 1 lot @ 1.2910
price goes down to 1.2900 you close the position and open
Buy 2 lots @1.2900
price goes down again to 12890, you close the position and open
Buy 4 lots @1.2890
Price hits 1.2900 you close and make $400 minus the $200 lost in the 2 lots and minus the $100 lost in the first trade yielding a $100 profit in the end. Many people dont like it because by the time you get to your 3rd trade you're down $300. And you're risking $400 more. Then spread goes into play and interest rates do as well so you end up with slightly more complex calculation but this is usually used by Roulette and Blackjack players as they double their stakes in order to make up for their previous losses