In one of my book reviews, I noted how the human brain is able to run in auto mode in certain situations (especially when pushed against the wall). It turns out that there is a name for this superpower: Unconscious Bias. According to here, unconscious bias are like mental shortcuts. Imagine you see a snake all of a sudden and unexpectedly, and you recoil from it. You might know that not all snakes are dangerous, and you might also know how to determine whether a snake is dangerous or not, but it is thanks to unconscious bias that you quickly tried to get away from it. In order words, in the unexpectedness of the situation, your brain assumed that the snake was dangerous. This trait might have evolved in humans (and whatever else animals have it) to protect them from danger.
In the same way, without thinking, humans also hold biases about other people based on certain things like skin color, tribe, dis(abilities), etc.
Designers must overcome these biases in other to champion inclusive and accessible designs. They must also seek to leverage the biases people commonly hold in order to create better experiences.