I have a kind of theory of humours for psychology which is just barely based on bits and pieces of science I've picked up over the years. Basically, it classifies people into dopamine- or serotonin-dominated people. Dopamine people are like extroverts, excited by new experiences and meeting new people. Serotonin people are more introverted, and likely to respond to new experiences with fear, thus taking fewer risks. I know psychology is way more complicated than that, and nobody is 100% either way, but we all like ways of classifying the people we meet, and this is one of those ways.
People who are problem gamblers apparently view a near-win as if it were a win, and get the same high from that as they do from an actual win. Some other people, apparently with non-addictive personalities, view the near-win as a loss, and get their reward moment from stopping. I wonder whether this has anything to do directly with brain chemistry. Addiction is tricky, of course, but if your brain has two potential responses to a stimulus, such as flooding with dopamine or serotonin, then those of us with serotonin responses are going to get a negative reinforcement.
I also wonder whether dopamine and serotonin people wake up differently. I think of myself as serotonin-dominated, and I wake up quickly, while Debbie is in the dopamine camp, and she wakes up very slowly. Of course, two data points don't make much of a pattern.
Mokalus of Borg
PS - I should probably read about serotonin syndrome.
PPS - Or I could just keep speculating wildly without any training, which is more fun.