We've come up with this rule after The Sacred Pool Expansion. The secret endings are hidden for players since the beginning, but after they complete a Warlock quest or when they gain fate above the starting amount, they either get facedown fate token (warlock q) or they can decide to turn down the fate they've gain in order to reveal the truth behind the secret ending. After gaining 6 (or whatever amount u want) of those "clues" they can secretly read the ending card to be ahead. We also add a rule, that after the completion of a warlock q, player must make a choice - either to take "a clue" or to gain normal reward from Sacred Pool Expansion.

Just sharing...