Hey Martingale is a old and tried and tested strategy, Martingale you'll find every second gambler has either tried it or will recommend based on his experience. Normally I'm not a big fan of this strategy as in the long run you go bust, plus this strategy has been tried mostly on dice not roulettes. While the guide is definitely good, I would advise you not to follow it as the probalties of you incurring looses are higher. As for your friend it could be purely a stroke of luck, as gambling requires loads of luck irrespective of the strategy.