I think magical chemicals are more picky, when simply mixing...Salt or Mercury(the most random things I can think of, I know) they don't care which way you stir, while in Potions that is important.
I've seen several spells that will do it to varying degrees, but none I want to do when I just woke up and can barely walk none the less speak coherently. Pushing buttons while angrily muttering angrily is much easier.