The answer is the overconfidence effect which is a very well documented cognitive bias. Cognitive biases are ways in which our thinking is inclined commonly at a very unconscious level. The overconfidence effect is correlated with another very common bias: conformation bias which is the tendency to only account for information that supports our believes while ignoring the rest of information. To summarize the over confident effect is the tendency to think that our abilities are far greater than they actually are, and we often uses the conformation bias to support this believe even in the face of very dramatic negative evidence.
