You've very nearly got it. Hypothetically speaking, lets say you had an advanced race of people on the verge of becoming psychic powerhouses, but were still immature. They were creating "monsters from the Id" just by thinking too hard about them. Fear of a giant evil sun. Fear of a statue that kills when you look away. It was creating a threat to the galaxy. You can't wipe the psychic race out, because if they learn your intentions they might think you into extinction. So instead you contain the race as best you can, wiping their memory of their place in the galactic stage, moving them home, and hoping that they stay put long enough to properly develop and cease being a threat. You can't convince them they're the only race in existence, because their power might alter reality to make it the truth. Goodbye all sentient alien races everywhere. You also can't fully convince them they don't have their powers anymore, because it might create some kind of paradox: if the power doesn't exist how could it destroy itself?
So you leave a handful of these psychics "in the know." You let them know what's up and they agree with your assessment: they needs to sit put and chill for another thousand years to get its head in the game, so to speak. A small group of psychics shall watch over things, to ensure that the species doesn't do anything catastrophic. You need to keep them from thinking aliens into extinction so you introduce a UFO, and suddenly people believe aliens exist. The rest of the galaxy is safe from obliteration. You don't want the race to convince itself its powers don't exist, so you introduce a ghost or a demon or a little girl with stars for eyes. You don't need these things to run rampant over the planet, that'd be dangerous. Just a few people exposed, here and there, who know enough to believe, and you've got yourself a psychic safety blanket. As long as the Indoctrination holds, the psychic race won't remember it used to be the next best thing to the God Emperor of the Imperium and start curb-stomping alien species with the power of their minds, strictly out of spite.
Secure humanity. Contain its power. Protect reality.
Does the Foundation catalog anomalies, or dangle them in front of our eyes like a carrot on a string?
