 In principle, we would like the molecule to be at low levels of energy, right? It's better to be good than to be bad. But the question is, what do we mean by good and bad? You would probably instinctively say that something here, if this is energy as a function of some arbitrary coordinates, being low is good and being high is bad. But how bad is bad? If that red peak was half that height, would that still be horribly bad? Or is it somewhat bad? And is that blue astronomically good or just a little bit good? We don't know. Second, you have two more valleys here. I didn't mark them as good. But does that mean that they're bad or not just as good as the lowest one? We don't know that either. And we're going to need some tools to start describing that or there is no way we're going to learn how to describe how molecules behave in practice. The problem is that that's not entirely trivial. There are a couple of examples that we can use to introduce that.