Treat your password like your toothbrush. Don't let anybody else use it, and get a new one every six months.

The comparison to a toothbrush compresses two norms into a memorable rule: passwords are personal (don’t share them) and they should be refreshed periodically (replace them). The humor works because it invokes a strong social taboo—sharing a toothbrush—to make password sharing feel equally unacceptable. The “new one every six months” line also reflects an older security doctrine that favored scheduled password rotation to limit the damage of unnoticed compromise. Today, many security guidelines prefer longer, unique passwords and rotation only when compromise is suspected, but the quote remains significant as a classic piece of user-centered security rhetoric: it aims to change behavior by making abstract digital threats feel concrete and bodily.