After the bare requisites to living and reproducing, man wants most to leave some record of himself, a proof, perhaps, that he has really existed. He leaves his proof on wood, on stone or on the lives of other people. This deep desire exists in everyone, from the boy who writes dirty words in a public toilet to the Buddha who etches his image in the race mind. Life is so unreal. I think that we seriously doubt that we exist and go about trying to prove that we do.
Proof is but a fallacy invented by man to justify to himself and his fellows his own crass lust and folly.