This is an excerpt from Married Man Sex Life Primer

The question is, “Why are Nice Guys so fixated on the wrong strategy when everyone else can see that it is failing them?” Even the Nice Guys can say they understand it’s the wrong strategy, but they persist in it anyway. An easy answer is that Nice Guys are simply psychically damaged from some sort of childhood trauma and can't break free of the early programming. Though that may indeed be true, that helps us little as an actual tool for change. The way I believe it is best understood as an adult is that the Nice Guy gets hooked into a behavioral response pattern to being given a random reward.

Imagine a lab rat in a cage that has a lever on one wall. If every time the lever is pushed a food pellet is given, the rat will only push the lever when it wants a food pellet. The rest of the time it will ignore the lever. If the lever does nothing, the rat will play with it, figure out it's useless and then ignore it. However if the lever randomly drops a food pellet into the cage, the rat will spend a lot of effort working the lever to ensure it has a supply of food pellets. It's the same basic principle that addicts people to gambling on the one armed bandit slot machines. You may pull the lever nine times and get nothing, but the tenth time might be a winner, or maybe not until the 100th pull.

It's random and creates a large dopamine response when it finally works. Sex already triggers a big dopamine response as a reward mechanism, so a randomized sexual reward is a double whammy and creates an utterly massive dopamine response. If a Nice Guy is in a low sex marriage, when he finally gets sex it creates the same sort of hormonal response as winning a good sized jackpot off a slot machine; it’s an intense and addictive high. For the Nice Guy, the problem isn't that he never gets what he wants; the problem is he sometimes gets what he wants. It’s not that she never has sex with him, but that she drip feeds it to him. Rather than understanding that the Nice Guy strategy is a losing strategy, he mistakenly believes that it is in fact a winning strategy.

Rather than altering the strategy he resolves to be even nicer to her. The thought process is that nice does affect her and that by being even nicer, she will reward him more frequently (i.e. "be in the mood"). After all, he thinks to himself... on the nights that she did have sex with him he was being nice, so nice must have an effect, so therefore... increase the nice! It's the same dopamine driven approach as someone buying not just one lottery ticket, but dozens in the belief that more chances to win are better. Or like the rat in the cage hammering on the lever that drops food pellets at random.