The authors of this book include several examples of the limits of everyday thinking, including not questioning authority, accepting "common sense" without questioning it, not questioning traditional beliefs, making generalizations based on one's personal experience, using only selective observation, and using biased observations. You can think about how these limits to thinking may have caused you to make generalizations about certain groups or people.
For example, people often do not question authority on a subject. In parts of the American South (and the rest of the country) during the Jim Crow years, whites were taught that African Americans were inferior. Many people did not question this idea, as the authorities around them (the schools, the media, and so on) disseminated it. People believed in the idea, which was regarded as "common sense" at that time, that the races should not mingle (even the idea of "race" is a fallacy), and they did not question traditional beliefs about race. People may have made generalizations about an entire race of people or group of people just using the few people of that race whom they knew. For example, they may have thought, "All African American people are like the few whom I know." This mistake in judgment would also involve using selective observation. For example, they may have only observed a few African American people in their towns or communities and not been aware that there were other African Americans working in government, the arts, law, medicine, and other fields. In addition, they may have made biased observations of the people they interacted with.
All of these limits to thinking would have resulted in confirming people's biases about African American people. Instead of looking for evidence in an objective way, they were only using their own personal experience and selective and biased observations. They were looking for examples of African American inferiority, and they felt that this idea was confirmed by what they saw. This idea was reinforced by the authorities around them. They did not collect hard evidence by looking beyond their personal experience to the wider world. Perhaps you can think of other examples of limits to thinking and explain them.