It depeds on which game you play. Card counting can certainly help but casinos don't like it. As far as roulette is concerned, betting on a color or on odds/evens gives you better odds than winning than if you were to bet on a single number.
If the casinos knew that you are doing this strategy and win in the game then certainly you will not be able to go get back on that casino again cause you make them lose money. Card counting is a big help to win but it is still a talent of someone to be able to remember all the cards. In other games, it would be base in pure luck so math would not be of help to any of this. If you are lucky on that day then good for you but if you are not then better go back another day when you are level-headed so that you can avoid spending more money trying to get back your losses.