I was pretty sure that trolls had something to do with it. They forgot to mention that the blade and quench tank need to be aligned with magnetic North and a full moon is preferable. Sacrificing a chicken or small mammal is often times helpful as well.
Of course none of this is true, and this leads me to this video from knifemaker and video-educator extraordinaire Walter Sorrells. He goes into the weeds a bit, but it is a great explanation of what is going on inside the steel when you heat and quench a blade.