It basically means that we have a tendency to believe that
things are going to continue on like they always have. Things will
always be "normal."
Anyone paying ANY kind of attention to history knows that's hardly ever true.
Normalcy bias refers to a mental state people enter when facing a disaster.
It causes people to underestimate both the possibility of a disaster
occurring and its possible effects. This often results in situations
where people fail to adequately prepare for a disaster, and on a larger
scale, the failure of governments to include the populace in its disaster preparations.
The assumption that is made in the case of the normalcy bias is that
since a disaster never has occurred then it never will occur. It also
results in the inability of people to cope with a disaster once it
occurs. People with a normalcy bias have difficulties reacting to
something they have not experienced before. People also tend to
interpret warnings in the most optimistic way possible, seizing on any
ambiguities to infer a less serious situation