Some mental shortcuts are certainly useful, and in any case unavoidable! We can't possibly process all the information that is available to us.

This book was specifically about racial bias. Whatever the many reasons for how racial biases arise, and whatever benign purposes they may sometimes serve, they do cause harm.

The author, a Black woman, grew up surrounded by only Black people, until at age 12 she moved to a majority-white town. A group of white girls were friendly to her, but she had trouble bonding with them because, to her, all their faces looked identical. She had never learned to distinguish white faces. In this case, her bias wasn't the result of firsthand interaction or secondhand teaching; it was her lack of prior interaction with white people. So, her bias wasn't the addition of falsehoods or bad feelings, but rather the absence of needed information. No matter how hard she consciously tried to learn these faces, her brain kept trying to exclude the information as irrelevant. The consequence was that she couldn't call her classmates by their names. Many people are not aware that their brains are racializing other people like this until the moment when they have to change and then they realize how difficult it is to change. The book is limited to this kind of deeply rooted racial assumption.