The quote on the white board was likely inspired by a medical book.

“Truth is like a surgery. It hurts but cures. Lie is like a pain killer. It gives instant relief but has side effects forever.”

This highlights the need and the urge to be truthful at all times. A lie can temporarily tide you through a patch but will catch up later to mess you up totally.

I don’t agree with lies being like painkillers as painkillers have a role in healing and comfort too without any side effects. Let’s just assume that there is a bit of artistic liberty in this quote for that aspect!