Well, first of all, those two substrate molecules that are about to react must actually collide. So they must collide, they must collide with enough energy and they must collide with the proper orientation. So only when the collision actually takes place with the proper orientation and with the right amount of energy do we actually form the product molecule. Now, what the active side does, what enzymes actually do is they bring the substrate molecules into this very small region of space that creates a microenvironment for that reaction. So inside the active side, we create a microenvironment that not only brings those substrate molecules in close proximity, but it also orients those substrate molecules in the proper orientation so that reaction can actually take place. For instance, if we go back to Covalent catalysis.