All the time. I taught myself rudimentary techniques for fixing decks as a kid in the hopes of making money but then found out that casinos use machines and multiple decks to prevent that.
So I'd hustle my mates in Presidents and Arseholes (I've heard it just called Arsehole). I also used them techniques to do card tricks for tips as a porter at work for a while. Was fun.
Anyway, to do that I'd have to play various card games against myself, usually playing as much more than 2 players too.
I also use to do the same with Pokemon cards as a kid because I was one of the only people I knew who actually played the game, most of my friends just collected and traded the cards.
I also played chess and checkers against myself.
Oh yeah, there was a Harry Potter card game I did that with too, in fact I use to invent card games which I would test on myself for weeks then test on my family and finally test on my friends. None of them ever caught on, but I spent a good 2-3 years of my life thinking about awesome card games I could make.
EDIT: I'd also run all of my D&D heroes in Highschool through a gauntlet which would test them in various combat situations at every level through to epic, that way I could plan out which feats, skills, and (if applicable) spells to pick. Usually I'd have an idea like: "I want to make a dual wielding nunchaku user." and I would try making the most efficient version of that hero using various classes to find the way I could become powerful/competetive most quickly without reaching my maximum power until at least level 17 (Maximum power being the point at which my ratio of damage/round/level:damage output/round/level gradient decreased from the last level up.). I enjoy doing that sort of basic math and problem solving.
So I'd hustle my mates in Presidents and Arseholes (I've heard it just called Arsehole). I also used them techniques to do card tricks for tips as a porter at work for a while. Was fun.
Anyway, to do that I'd have to play various card games against myself, usually playing as much more than 2 players too.
I also use to do the same with Pokemon cards as a kid because I was one of the only people I knew who actually played the game, most of my friends just collected and traded the cards.
I also played chess and checkers against myself.
Oh yeah, there was a Harry Potter card game I did that with too, in fact I use to invent card games which I would test on myself for weeks then test on my family and finally test on my friends. None of them ever caught on, but I spent a good 2-3 years of my life thinking about awesome card games I could make.
EDIT: I'd also run all of my D&D heroes in Highschool through a gauntlet which would test them in various combat situations at every level through to epic, that way I could plan out which feats, skills, and (if applicable) spells to pick. Usually I'd have an idea like: "I want to make a dual wielding nunchaku user." and I would try making the most efficient version of that hero using various classes to find the way I could become powerful/competetive most quickly without reaching my maximum power until at least level 17 (Maximum power being the point at which my ratio of damage/round/level:damage output/round/level gradient decreased from the last level up.). I enjoy doing that sort of basic math and problem solving.