I've been using these strategy the first time I gambled on gambling sites, this is a common strategy on my early experiences on card games when I am gambling with my cousins though we are betting something like marbles and not money. This strategy is a high risk high return strategy though, I agree that people must not do it since gambling is not a sure way to get a good profit.
Right, I also used this strategy on my early years of gambling. However, we all now that the success really depends on luck. So it's still 50/50. I used variations of Martingale, but I wouldn't say I'm completely satisfied by it though. Its really up to us if we wanted to stick with one system or just bet with your instinct and see how it goes for you.