The incompleteness hook leaves a task, story, or process deliberately open so the unresolved state keeps you mentally returning to it. The observable structure is a loop opened and left unclosed: a partly filled progress bar, an unfinished profile, an interrupted narrative, a running streak, a saved-but-unbought cart.
The unresolved state is meant to occupy the mind between sessions and to make closing the loop feel like relief — which the technique then routes toward whatever action the sender wants: returning to an app, buying, re-engaging, continuing to the next monetized unit. It differs from the curiosity gap, which withholds an answer; the incompleteness hook leaves an action or state unfinished. It is the broader, often non-narrative sibling of the cliffhanger.
The honest / manipulative line: whether the loop, once closed, serves your goal or merely re-hooks you into another open loop. Note the evidence is contested — the classic Zeigarnik recall effect replicates inconsistently, so the pull is real-but-unreliable, not guaranteed.