He knoweth our frame; he remembereth that we are dust. The word translated frame is the potter's word — the shape a thing was formed into. God is not disappointed to discover our limits. He set them.
We forget this constantly. We plan as though we do not need sleep, commit as though we will not get ill, and then treat our own tiredness as a moral failure. Much of our self-condemnation is really just an argument with the fact that we are creatures. We wanted to be more than dust and we are offended to be reminded.
The psalm puts this fact in the middle of a passage about mercy, not judgment. God remembers we are dust and the conclusion he draws is pity: like as a father pitieth his children, so the Lord pitieth them that fear him. Our frailty moves him to tenderness rather than impatience. He is not standing over us tapping his foot, waiting for us to become something sturdier.
There is freedom in accepting the frame you were made in. It lets you say no without guilt, rest without justifying it, and ask for help without treating it as defeat. And it puts your hope in the right place — not in your own durability, which is grass, but in a mercy the psalm says is from everlasting to everlasting.