Optimism Bias is a cognitive bias that causes someone to believe that they themselves are less likely to experience a negative event. Optimism bias is common and transcends gender, ethnicity, nationality and age. Four factors exist that cause a person to be optimistically biased: their desired end state, their cognitive mechanisms, the information they have about themselves versus others, and overall mood. The optimistic bias is seen in a number of situations. For example: people believing that they are less at risk of being a crime victim, smokers believing that they are less likely to contract lung cancer or disease than other smokers, first-time bungee jumpers believing that they are less at risk of an injury than other jumpers, or traders who think they are less exposed to losses in the markets.
One useful counter-measure is to ask: What data am I using to base my optimism upon? Are there any more rational ways of assessing probable outcomes that using the data points I have access to?
For a full list of the most common biases, click here.