Illusion of invulnerability is best defined as the mindset that one cannot be harmed by anyone or anything. This type of thinking may cause people to take more chances or risks in their lives.
This phrase is associated with psychologist Irving Janis, who specializes in groupthink study. The phrase is often used to describe homeland security oversights, such as the belief that a terrorist attack could not happen on American soil. Many people still feel that America is untouchable an invulnerable, even after the terrorists attacks of 9/11. Having such a mindset can lead to a false sense of security.