and as for what he means, I think it's about needing a witness to one's life. I've always thought he was vulnerable to being known - as are most of us at that age - and so the less you know others, the less they can know about you and the less you need them.
The question is whether or not a solitary life actually provides a greater sense of self-actualization.
The mistake most people reading this book take away is that it's all about saying "fuck you" to the world, more or less. That always seemed way too easy to me. He defined a generation, the character that is, but I'm not altogether certain that J.D. intended that to be the battle cry.