How do you know if it's paranoia or instinct?

Where's the line between instinct and paranoia? Experience and questions on one side, fear and assumptions on the other.

Life used to be simpler ... Are you sure?

I used to think life used to be simple but now complicated. I don't think that anymore, I think life always was complicated but it was simple in our options how to deal with it.
Simple doesn't necessarily mean easy.