The key issue was that no reason could be found.
Sometimes, even when something felt amiss, the elixir still turned out successful, and could even burst forth with a high-grade quality.
Although this was a low-probability event, you couldn't rule it out, given the sheer number of elixirs an alchemist would produce in a lifetime; encountering it three or five times made people gradually accept this notion.
Of course, this probabilistic event referred to the production of elixirs of the same grade: a First Grade Alchemist making a First Grade Elixir, a Second Grade Alchemist making a Second Grade Elixir, there's no such mysticism about lowering one's realm to do so.
Bathing and burning incense, paying attention to the weather...
This had become a necessary procedure for many alchemists before they concocted some important elixirs.
Some extreme alchemists, it is said, even sought to bed virgins before alchemy.
