Sin lies only in hurting other people unnecessarily. All other "sins" are invented nonsense. (Hurting yourself is not a sin — just stupid.)

The remark reduces morality to a single, secular criterion: avoid causing unnecessary harm to others. In doing so, it rejects religious or culturally inherited catalogs of “sins” (especially those centered on private behavior) as arbitrary social inventions rather than intrinsic moral truths. The parenthetical aside draws a sharp line between ethics and prudence: self-harm may be foolish or self-defeating, but it is not morally culpable in the same way as harming another person. The quote thus expresses a libertarian-leaning, harm-based ethic—akin to a stripped-down “harm principle”—that privileges personal autonomy while insisting on responsibility where one’s actions impose costs on others.