<span>It's because the process is not as organized as we have learned it. We tend to think of intracellular reactions as they're supposed to work. Only thymine is supposed to bond to adenine. Only a specific type of ligand bonds to a certain receptor etc. this type of thinking leaves it hard to imagine what's actually going on. Imagine complete and utter chaos. Enzyme being hit by all the wrong and right molecules many many times per second. Molecules flying off in every which direction and hitting against anything and everything. When we learn about these reactions we tend to think it's ordered based on how specific things are. Not only is an enzyme/protein site made to fit only a specific molecule, it has to be the correct orientation. So even if the right molecules are in the right place hitting against the right enzyme does not mean it will attach, assuming it doesn't approach at the right angle.</span>
