Few interviews were conducted with the truth-telling potion. Not only was the potion expensive and time-consuming to brew, it was less fun. If a person knew to expect a cup of tea with a potion in it, they would be less likely to be deterred from the very activities the regime was trying to prevent in the first place. Fear was a powerful motivator. Only in the cases, like poor Rosalind's, where the person was innocent did they even consider the more humane option.