Cognitive biases are unconscious mental shortcuts that pull reviewers away from objective judgment — and they’re extremely common among managers writing performance reviews. Recency bias weighs an employee’s last few weeks far more heavily than the full evaluation period. Halo and horn effects let one strong or weak trait color everything else about that person’s review. Similarity, or affinity, bias unconsciously favors employees who share a manager’s background, personality, or communication style. Central tendency bias clumps everyone toward “average” to avoid hard conversations. Leniency or strictness bias rates everyone too generously or too harshly across the board. And confirmation bias means a manager enters the review already believing something about an employee and only notices the evidence that confirms it.