Normalcy bias, or normality bias, refers to a mental state people enter when facing a threat or 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.