From the left, it's approaching negative one, or it's constantly negative one, and so it's approaching negative one, you could say. And from the right, it's one, and it's approaching one the entire time. And so we know if you're approaching two different values from on the left-sided or the right-sided limit, then this limit will not exist. So here, this is not differentiable. And even intuitively, we think of the derivative as the slope of the tangent line, and you could actually draw an infinite number of tangent lines here. It's one way to think about it. You could say, well, maybe this is the tangent line right over there, but then why can't I make something like this the tangent line?