When I was in the third grade I sort of cheated on a multiplication table test. It was for the 8s, so we were supposed to memorize 8x1 through 8x10.
For some reason, I could not remember that 8x7 was 56 and kept thinking it was 58. So to remind myself, I got one of those novelty oversized star-shaped erasers you can stick over the actual eraser on your pencil (actually don't know if those are still around since I guess they're a choking hazard, but they were still around in the 80s). On this giant star eraser I wrote "56" to remind me of the true answer.
The tests were passed out, and I got all of mine right. I didn't even have to look at the eraser because the act of writing 56 on it had caused me to remember it anyways.
When the teacher collected the test, I was all "oh shit, I didn't technically cheat but I did give myself a safety net and the evidence is right there so I'd better get rid of that real quick just to be safe."
So I removed the eraser from my pencil and took to trying to erase the 56 from the eraser. Erasing stuff off an eraser turned out to not be that simple. Suddenly the girl sitting to my left exclaims to the class "Lars cheated! He wrote the answers on his desk!"
Palming the star-shaped eraser I quickly retorted with my best 3rd-Grader Squeal of "No, I didn't!"
Technically I was telling the truth since she mistakenly thought I was trying to erase the answer from my desk.
In an instant half a dozen students were crowding my desk, scanning it's surface for answers. At the time I was a Straight-A student and probably had the highest or second highest grades in the class, so of course they were more than happy to find out I cheated.
I calmly slid the eraser from my palm into my desk while they were scanning for answers on the surface of the desk. I was confident they wouldn't find anything because I knew I hadn't written anything on the desk.
Suddenly a kid slams his finger on the desk, "He did! Here's a number nine!"
Shocked, I looked down. He was pointing at a number nine drawn on my desk. Shit.
"I didn't put that there!" I shouted back. The kids didn't buy it, they thought they had caught one of the nerds red-handed and were going to make sure it stuck. I was actually proud of my little eraser-cheat plan and was actually a little insulted they thought I had simply wrote the answers on my desk, and I very nearly foolishly gave myself up just to prove them wrong (such is the logic of a third grader).
Instead I realized something else. Eight is an even number.
"Nine isn't even a part of an answer to any of the questions!" I shouted to the class.
The teacher, still at his desk, reasoned that if I knew off the top of my head that nine wasn't in any of the answers that I probably didn't cheat.
The classmates still wouldn't let it drop. The one who had discovered the name said something to the teacher along the lines of "If this had been me you wouldn't have given me the benefit of the doubt!"
At this point I was a mixture of emotions. I was pissed off from being accused, insulted that I technically did it but in a more clever way than I was being accused, terrified of being caught for real, emboldened by the teacher essentially siding with me, and determined to shut these kids up good. So I got up from my desk, walked up to the chalk board, and quickly inscribed out "8x1=8, 8x2=16, etc." all the way up to 8x10. It was easy since I'd already memorized nine of the answers, and there was no way I was forgetting 8x7 after this.
When done, I turned back to my accusers and asked, "So how did I cheat that time?" This shut them up, I got 100 on my test, and got to be smug about it (as well as the fact I hadn't been caught). All in all, a good day for someone who at the time was a friendless (yet arrogant) nerd.
And that's my story about cheating.
tl;dr: Cheaters prosper as long as they don't get caught and brazenly deny it when they do.
Though I think cheating on someone you're in a real committed relationship with is pretty bad. Even if you don't get caught.