If someone does something evil, let them not repeat it; let them not desire it; accumulating evil produces suffering.

Na taṃ kayirā punappunaṃ — let them not repeat it: the first step after an error is not self-flagellation but the decision not to repeat it. Repetition is what converts the isolated act into habit and habit into character.

Na tamhi chandaṃ kayirātha — let them not desire it: deeper than action is intention (chanda). It is not enough not to do evil; one must work for the desire to do it to weaken. Practice works at the root.

Dukkho pāpassa uccayo — accumulating evil produces suffering: uccaya is accumulation, piling up. Like compound interest on debts, accumulated bad actions produce an increasing weight of suffering.

Buddhist psychology distinguishes between the isolated act (not disastrous) and the habitual pattern (which forms character). The work of practice is precisely to interrupt these patterns of repetition before they solidify.