If we accept that a lot of things may ultimately not be about our senses but rather about the chemicals released in our brains in response to our senses... well, then we can begin to understand so much, like what happens when the process goes awry. People realize, because they've witnessed the effect on peers (on TV if not in real life!) that drugs have a detrimental effect on the reward/ motivation system. Most of us, though, have less experience with people whose brains that work like that naturally -- people whose reward systems aren't triggered normally by their senses, but instead respond to only a limited set of stimuli. (It doesn't occur to a lot of people that that way of being even exists at all.)
I told a friend once that what looked like excessive fear on my part was actually monotropic vulnerability. I'm not sure the distinction was clear. I meant that if a person's reward system is triggered in unnaturally strong ways by just one or two stimuli -- and if they fail to respond to other supposed rewards -- then an unnatural amount of their attention is going to be focused on those one or two things.