Poker or roulette is the same, the only difference is that you need to know a bit about poker and to be lucky to have good cards, that's all.
In fact, they have nothing in common.
1-roulette is a game in which you play against casino. Statistic advantage is on casino site so it is impossible to win in long term no matter what system you have ... martingale too (
https://bitcointalk.org/index.php?topic=5177375.msg52217862#msg52217862)
2- poker is a game in which you play against other player. None of the players have statistic advantage. Any skill (counting odds and money management f.e.) allows you to earn in long term where luck does not matter (after infinite amount of games every possible card set will hit you good once, bad once - the key to earn is to win as much as it is possible on good once and loss ass little ass possible with bad once) - You can read more here -
Play poker to train trading