Why do you use triangles?
I like geometrical structure. The lines help your eye to move all around the painting without sliding off the edge.
Can you give an example from this painting?
The two equilateral triangles make the middle of the picture feel calm. The one that points up gives the figures a relationship even though Mary is looking away. The long sides of the other triangles all point at the top right as though the story will continue in the maze and the castle.
Why are they hidden?
If they were obvious they would distract you. I want you to sense the effect of the structure but not see just triangles.