It might be that the dumbest person is still contributing productively. They'll just be contributing the least.

This is true. I was thinking, though, of the purely emotional impact on someone who is used to being the smartest person in the room to suddenly finding himself the least smart person in the room. Specifically, it's a lesson I have had to learn myself -- for me, it was a lesson I started learning in high school, and have re-learned the lesson many, many times since then. It's not a fun lesson.