This is a spiritual world. The most ruthless yet rational rules of the game: the winner is the king, the loser is the bandit.
If you forget to be strong, you will become weak;
If you forget the sadness, you will no longer shed tears;
If you forget loneliness, will you lose yourself?
If you forget the past, there will be no future;
(Maybe it's a little different from the Shaman King anime)