The evil done by oneself, born of oneself, produced by oneself, grinds the fool like a diamond grinds a gem.

Attanā va kataṃ pāpaṃ attajaṃ attasambhavaṃ — the evil done by oneself, born of oneself, produced by oneself: the triple insistence on the self-origin of evil. Attaja (born of the self), attasambhava (produced by the self), attanā kataṃ (done by the self). There is no escape or transfer of responsibility.

Abhimatthati dummedhaṃ — grinds the fool: abhimatthati is to grind, pulverize, crush. The verb is violent because the dynamic is violent: one’s own harmful actions pulverize the one who generates them.

Vajiraṃ vasmamayaṃ maṇiṃ — like a diamond grinds a gem: vajira is diamond (or Indra’s thunderbolt). Asmamaya maṇi is a stone gem. Diamond, the hardest substance, is capable of destroying gems of apparent value but softer constitution.

The image is doubly meaningful: diamond is one’s own action (karma), and the gem it grinds is the exterior brilliance of the fool who, despite attractive appearance, cannot resist the weight of their own actions.