"Normalcy" bias is the mental state that people can enter when facing a disaster. It is similar to an altered state of consciousness when one adapts to a drastically different set of circumstances. This tendency to change "mentality" in the face of disaster causes people to underestimate the possibility of disaster and its effects. If you've ever been in a drastically changed circumstances; sudden hospitalization, an evacuation for a fire, flood, or earthquake, etc. you will be able to identify with this bias.