When you see your first zombie, at first you don’t quite understand. You feel confusion: it’s a person, but something’s wrong. Then it becomes clear that it’s not a person anymore. That’s when the terror starts.
If you live through that first encounter, terror gives way to nagging fear and determination. Then, steadily, you build confidence.
That leads inevitably to complacency. You make mistakes. Eventually, one of those mistakes gets someone killed.
If that someone isn’t you, you go back to the terror.
This cycle repeats over days, weeks, months, until you are completely numb, feeling nothing but your exhaustion.