“A little water clears us of this deed.”William Shakespeare · Macbeth · 1606 · Actul II, scena 2
Guilt lives in memory, not on the skin, so no washing removes it.
She reduces the crime to a technical mishap: if the hands are clean, the act is gone. The mechanism is a classic error about conscience: guilt is not on the skin but in memory and imagination, so no external agent removes it. The play confirms this later, when the same woman washes her hands in her sleep and finds no scent that cleans them. A concrete case: someone lies, then buys themselves something nice to feel better, and discovers the mind refuses the trade.
Why it matters The line works as a warning: symbolic gestures of cleansing after a wrongdoing do not work; the only real remedy is owning up or making amends.