An Itch You Have to Scratch

Have you ever found yourself humming a catchy song, but you can only remember the chorus? It drives you crazy until you finally look up the rest of the lyrics.

This is the Zeigarnik Effect. Back in the 1920s, Soviet psychologist Bluma Zeigarnik observed that waiters had a flawless memory for unpaid orders, but forgot them the second the bill was settled. Human brains despise unfinished tasks—they linger in our subconscious, constantly nagging us.

In UX, this is one of the most powerful retention tools available.