Nothing about the facts changes. The rent is the same, the diagnosis is the same, the person who left is still gone.
What moves is the frame. The same photograph cropped two inches wider includes the person standing just off to the side, and suddenly it is a picture about something else.
That is the whole mechanism, and it is less magical and more useful than it usually sounds. Gratitude does not delete what is difficult. It widens the frame until the difficult thing is one element in a larger scene rather than the entire scene.