We're not talking about endpoints right now. We're talking about when we have points in between, or when our interval is infinite. So we're not talking about points like that or points like this. We're talking about the points in between. So if you have a point inside of an interval, it's going to be a minimum or maximum, and we see the intuition here. If you have non-endpoint min or max at, let's say, x is equal to a. So if you know that you have a minimum or maximum point at some point x is equal to a and x isn't the endpoint of some interval, this tells you something interesting, or at least we have the intuition.