Our slope jumps here. And because it's not differentiable, the mean value theorem doesn't apply. Now you can imagine if this was differentiable, if this did have a continuous derivative, then you would find a point. 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.