A single misplaced detail—a subtle motion, an off expression—can push perception across a boundary and shatter believability in an instant. And once broken, perception does not easily reset. Minor deviations in realism can trigger a rapid shift from acceptance to discomfort, and those violations are deeply encoded in memory. Even if corrected in later frames, the initial mismatch lingers, coloring every subsequent moment and eroding trust. For creators of avatars, animation, and generative media, avoiding the uncanny valley is not optional—it is essential.