You keep him in perfect peace whose mind is stayed on you, because he trusts in you.
"Perfect peace" sets a high bar, and the mechanism Isaiah describes for it isn't circumstance-management, it's fixed attention: whose mind is stayed on you. Not whose life is sorted out. Not whose problems are solved. Whose focus doesn't wander off the one thing steady enough to hold it.
That's a hard ask if your mind is anything like most people's, pulled in a dozen directions by things that genuinely deserve attention. But notice the second half of the verse: because he trusts in you. The peace isn't self-generated through concentration technique. It's the natural result of actually trusting the object your mind is fixed on — which means the peace is only as available as the trust underneath it is real.
If your mind rarely stays still on anything for long, this verse isn't offering another discipline to fail at. It's pointing at what the stillness would actually be resting on, if it ever did settle.
If perfect peace sounds out of reach, it might help to ask what your mind would need to trust for that kind of stillness to even be possible.
A short video on this is coming soon — for now, read on.