Prejudice. Very few words raise the blood pressure as quickly in this hyper-aware day and age. Yet for all our awareness of prejudice in others, we don't always see it within ourselves. The very thought inspires a mental flinch, and an indignant "No, I'm not!" Yes; yes, we are, every single one of us.
From Dictionary.com: "any preconceived opinion or feeling, either favorable or unfavorable." We are the sum of our experiences; by our very nature, we measure new experiences based on... the rest of the story