The article talks about his ability to be friendly to strangers but abusive to his long term acquaintances. I have observed this pattern and curious if anyone knows what drives this? My personal theory is that you have some sort of obligations to long term acquaintances but you owe nothing to strangers on the trail. It's this feeling of obligation that leads you to resent people over time.
I believe it's called a mask. People with some personality disorders gradually develop a sort of behavioral mask to wear in public in order to fit in into the wider society and be able to achieve one's goals. However, having it 'on' is apparently taxing, so it comes off around people who are in one way or another part of some inner circle for whom there's no point to pretend.
It is indeed fairly common. I'm affected (thankfully not strongly these days) by bipolar behaviour. I try to present a more average me as the mask.
> in order to fit in into the wider society and be able to achieve one's goals.
It can be more selfless than that. In work life it is about fitting in (or at least not standing out in an inconvenient way) but in personal life it is more that I don't people to worry overly. I have things well managed, I know I can push through, I know it will pass, there is no need to cause stress in others.
> However having it 'on' is apparently taxing
During a bad patch, the extra concentration adds up over time if you find yourself having to work at it for a while. I don't have many prolonged bad patches, I imagine it can get exponentially harder for those more severely affected than me. It is why a lot of people experiencing mental health issues retreat away from interaction even if they are not otherwise particularly introverted.