The first chemist orders a H2O — which is water. We can drink water. We need it to survive.
However, the second chemist orders a “H2O too”, which sounds like H2O2, which is the chemical formula for hydrogen peroxide.
Now hydrogen peroxide is toxic to our bodies, and that’s why anyone who drinks liquid H2O2 is essentially committing suicide.
But the problem in the energy generation process is that the electron transfer has to be darned near complete to get oxygen molecules completely reduced to water.