This is the inhibitor, and this is the substrate. Notice that they are very similar in their structure. And that's precisely why when we mix these three molecules, that inhibitor will bind onto the active site, forming the enzyme inhibitor mixture. And so this substrate will not bind onto that active site simply because there is no space to actually go into that active site. Now, the question that you might ask is, why is it that the red molecule, the inhibitor, binds into the active side and not the green molecule, the substrate? Well, because normally the affinity of that inhibitor for that active side is much higher than the affinity of that substrate.