The overconfidence bias is the tendency people have to be more confident in their own abilities, such as driving, teaching, or spelling, than is objectively reasonable. This overconfidence also involves matters of character.
Generally, people believe that they are more ethical than their competitors, co-workers, and peers. For example, a recent study showed that 50% of business people polled believed that they were in the top 10% ethically.
Because of the overconfidence bias, people will often take ethical issues lightly. They simply assume that they have good character and will therefore do the right thing when they encounter ethical challenges. In fact, studies show that the overconfidence bias causes people to overestimate how much, and how often, they will donate money or volunteer their time to charities.
So, overconfidence in our own moral character can cause us to act without proper reflection. And that is when we are most likely to act unethically.