The Potion

When Twilight approaches Zecora about mass producing the potion that allowed her to see into the past, Zecora uses a similar potion to show her the consequences it could have in the future.

Zecora's potion allowed Twilight to briefly look into the ancient past, and now she wants more. When she asks for help in mass producing it, Zecora uses a similar potion to give her a glimpse into a possible future, where the costs of her endeavor may outweigh the rewards.