I know how it feels to be somebody like that. Although to a lesser degree than Adam Lanza, I AM somebody like that. Here's what it's like: You see the kids around you, laughing, playing, having fun. You want to join them, but some intangible barrier stops you. You don't understand it and you can't even describe it, but it's always there and keeps you apart. If you try to get through it or around it, your attempts are somehow off the mark, inappropriate, clumsy, and make others uncomfortable. Their discomfort leads them to ridicule you at best or shun you at worst. The world outside your head is painful; you retreat to the sanctuary of solitude. After a time you no longer want to escape your imprisonment.
You never fit in. You can't figure out how social interaction works. You suspect that everybody has knowledge to which you don't have, will never have access.
If you're lucky, compassionate others observe your plight and teach you how to act--they provide tools and perhaps medication that reduce the barrier's impenetrability and give you some perspective on the world out there. These aids get you through the day, but at the end, you know it's an act and although you're grateful for it, it is never an easy part to play. Parties drain you and you always quit the scene as soon as you can. Interactions with others leave you with unwarranted and relentless anxiety. If you learned well, your shortcomings withdraw into near imperceptibility and you lead what appears to be and even feels to you like a normal, comfortable, happy life.
I am one of the lucky ones. I think Adam Lanza was not.
12/31/12 - They ("Who are THEY? They are no damn good!" ~ Rhett Potter, psychiatric social worker, Weber County, Utah Department of Public Health, circa 1967) say part of emotional health is expressing oneself constructively, especially when one is ticked off. The goal, presumably, is to solve a problem in a way that nobody gets hurt.
That's tricky, especially in the heat of emotion. Once the bad chemicals borne of pent-up vexation accumulate, it takes time for them to clear out. Until they do, one's goal is likely to be something similar to mutually assured destruction.