When people often blame an "act of nature" or their colleagues for their plans going awry, they are illustrating the cognitive bias known as the overconfidence effect.

Blaming external factors such as an "act of nature" or colleagues for plans going awry is an example of the self-serving bias, not the overconfidence effect. The self-serving bias leads individuals to attribute their successes to internal factors and their failures to external factors. The overconfidence effect, on the other hand, is a bias where people overestimate their own abilities or the accuracy of their predictions.