Why do I get paranoid about interacting with police when in reality I rarely have encounters with them?

I'm not sure where you're from, but here, a person's socioeconomic situation and race can play heavily into how some of those interactions are going to unfold. It's an unfortunate reality and there is a legitimate reason for certain individuals to fear the police. 

  I know nothing about you nor about the overall situation to be able to answer this in any useful way. It’s possibly rooted in your life experiences, upbringing, history with authority figures, real or imagined guilt, etc. 

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I have no idea, and I don't know how you can figure that out by asking randos on the Internet like us.