The phrase "I must be cruel to be kind" suggests that sometimes, in order to truly help or be kind to someone, one may need to take actions that appear harsh or unkind in the moment. This often reflects the idea that honesty or tough love can lead to a better outcome in the long run, even if it feels cruel initially.
Given this interpretation, the "hidden truth" the paradox might be making is:
a. Sometimes being kind requires being honest, which can feel like cruelty.
This option captures the essence of the paradox, as it emphasizes that honesty, even when it may hurt someone temporarily, can ultimately be a form of kindness aimed at their greater good.