Some people are skeptical that they could have a problem without being aware of it. If it's bad, wouldn't that get their attention?
People have limited attention and have biases. Sometimes people are blind to the truth or grow up with an idea and never question it. And often people know they have an idea, value or personality trait, but they don't accurately know its consequences and implications.
The full consequences of actions are often subtle, complicated or hard to understand. Sometimes they are controversial. Is our choice to build factories going to destroy the environment? Should you get a Mac or a PC? Should we regulate the economy more or less? Should you be a Christian? Who should you marry? Even if you are aware of your decisions in these areas, it may still be hard to tell what is best.
One thing we do know is that whenever two people disagree about something, at least one of them is mistaken. Two contradictory ideas can't both be true. Since disagreement is common, mistakes must be common too.