@Tikibo, in my prespective that is just a self re-discovery story and how he become an Egoist. He was passive in his 'normal' life because he only think to get by each day and follow society Norm. He never doubt anything about the society normalcy and think he should follow the society norm, work, go home, go to work, go home till the end.
When his everyday live disturbed, he began questioning society normalcy and his position in it. So after he doubt it and began questioning the meaning of his 'normal' he began to defy the norm by commit suicide. Commiting suicide in Japan mean is very taboo because that is showing that you have up on something so he act again the taboo. But by commit suicide he also with the Norm of society, that people without greater meaning should just die. After he failed his suicide, he want to live with hardship, but there is two interpretation.
First, he actually want to die but angry with the fate to defy anything from him that include easy dead, so he would live till the fate give him the dead that he want. Or the second interpretation is he realize that he don't want to die and he was just commit suicide because he was shocked from disappearance of his life meaning and decide to keep on living till he couldn't defy the fate of death itself. So on both case he decide to live in wilderness because he ,his ego, and himself want and decide to do it.
He was never value his 'normal' life much because he was just following other people deed. That explain why he don't want to learning how to be more efficient at work at the old age. That also explain why he become very efficient in the wilderness. He live on wilderness because that is himself that want to do it not the normalcy of the society that 'force' him to do it.