It sounds like he had ADHD. Some people (and I'm using that term to include all genders here) cannot handle discomfort, and my speculation is that this is caused by chemicals in the brain.
Handling discomfort is a skill we must all learn, and different skills are required to manage different kinds of discomfort. Because we all vary in our degrees of sensitivity to different unpleasantnesses, and because our life paths give us more or less exposure to the experiences which cause them, some people get quite far into adulthood without learning to manage forms of discomfort others have been handling since childhood: but it is not necessarily the case that they cannot cope with those discomforts, in some ultimate sense, just that they have not yet learned the trick of it. Often there is some habitual pattern of avoidance which must be unlearned before that can happen.