So if this looks something like this instead, I'll continue it over here. If it looks something like this instead, where it had a continuous derivative, then there would be a point where the slope was the same as the average slope. Maybe it would have been right over there. So it's really because f is not differentiable over the entire interval. It does not have a continuous derivative. The derivative jumps from a positive value approaching zero here, and it just jumps straight down to negative two right over here. It doesn't go continuously through all the values in between.