Imagine telling a person something that goes contrary to their conditioning, to their beliefs. They would tend to dismiss it completely and choose not to take it into account, even while knowing it's true.
This is widely visible as a very real thing and why charlatans are able to be charlatans. Not sure why it is phrased as something that needs to be imagined
parent was being sarcastic
you have to go a level deeper, and plant the most basic version of the thought, just a seed, so that it grows and they think it's their own idea