Write it down.

Review it first thing in the morning, the better to remember it through the day at the moments when it will matter.

Review it last thing at night, to see if you remembered it that day and what difference it made.

I've discovered an area of likely self-delusion and I want to prevent myself from backsliding through forgetting what I've learned. Any ways to make sure the knowledge stays in my head?

Find something you can do that's consistent with the new belief and inconsistent with the old one. Ideally the action will involve other people since many of our beliefs are held in part for the purpose of manipulating other people, and it won't be just talk. Perform the action. The resulting cognitive dissonance will help to keep you in line.

(This is an extrapolation from the procedure for getting rid of specific self-deceptions in Anatomy of Peace, sort of. The author of that book knew that you have to do something with your insight to avoid losing it, and gave lots of examples, but he apparently didn't notice that the examples all fit the general rule I state above.)

Use an SRS. I've added personal insights and useful advice to my normal daily reviews and it works. I simply put the insight (and as many steps leading up to it as possible) as the question, leave the answer empty and rate it on how well I'm currently following / remembering it.

Perhaps writing down your notes in Anki so they come up every once in a while?

Find a real-life human you can trust to give you honest feedback about this area (partner, best friend, mom, etc.) and have them evaluate it from time to time. This works well for my wife and I (e.g. "You're probably being depressive about that issue, try re-evaluating.")

but suffice to say that I've discovered an area of likely self-delusion and I want to prevent myself from backsliding through forgetting what I've learned.

It probably doesn't suffice. There is an obvious piece of advice about not-forgetting, namely use of a spaced repetition system, but this assumes that remembering a piece of knowledge is actually what you need.

You could tattoo it across your chest, Memento-style and see it every time you shower. That might help you remember.

I'm somewhat reluctant to talk about my personal life online nowadays, but suffice to say that I've discovered an area of likely self-delusion and I want to prevent myself from backsliding through forgetting what I've learned. Any ways to make sure the knowledge stays in my head?

With great difficulty. At least in terms of embedding the real time habit of thought. The abstract knowledge isn't too easy to keep.

If it is a kind of general self-delusion that is a common topic subscribing to a blog on avoiding the delusion can be useful. As can general blog on habit changing.

Just make sure you stick to one area of 'self-delusion' at a time. Don't try to change everything at once.

The first thing first to do is to compress the information you need to remember (not coding-compress, that is, but eliminate the redundant parts).

If the knowledge has practical implications, invent a game whose winning strategies depend strongly on the information you want to remember, in a neat isomorphic way, and set yourself to become a master of that game.

Otherwise you could simply write down how your life could be in the future in both cases, whether you remember and correctly apply the information or not, and expand the narratives as your life goes on.

If instead the notions are simply formulaic, you could just as well use Anki, as already suggested.