A concrete example would be developing facial recognition algorithms. There are now several examples of them not working with black faces. It's definitely a lac

A concrete example would be developing facial recognition algorithms. There are now several examples of them not working with black faces. It's definitely a lack of diversity of thought to not think about whole segments of society when designing such things. At the very least diversity of physical characteristics on the development team would help remind them they exist. More usually its that physical characteristics represent lives that are inaccessible to people without them. So people with different skin color, disabilities, sex, gender and background are all reasonable proxies for diversity of thought by the fact that these people all have very different lived experiences.