The otherworldly must behave as their stage dictates until the power becomes part of them. Until the potion is digested, the bearer is vulnerable: the power is already there, but they have no control over it yet.
The roles of the path are tied to risk and stakes: the bearer repeatedly puts the outcome on the line and learns to live with what they are dealt.
The method long remained the knowledge of the few: church hierarchies were in no hurry to reveal it, and many otherworldly ascended blindly, paying for it with their sanity.