Largely this is a class thing - writers tend to be cosseted little middle-class kiddies who think that the world owes them a royalty cheque. But just doing it - being in your room for years on end locked in your head alone with invented ghosts - it weakens and softens the body. And I know I can't just live in my head.
The two most misused words in the entire English vocabulary are love and friendship. A true friend would die for you so when you start trying to count them on one hand you don't need any fingers.