Yes you are right, physical cursings do not depend on the mercy and grace of God. Adam and Eve brought misery and cursings on themselves by their bad choices. And then every human being that ever lived after that did the same, except Jesus Christ.
But to be delivered from physical cursings does depend on the mercy and grace of God.
God does not owe us anything, but we are forever indebted to him. He doesn't owe us rewards for good choices, but by his grace and mercy he enables us to make good choices and then by his grace and mercy he often rewards us for those good choices.
The point is if we find ourselves blessed in anyway, we can know that it is by the grace and mercy of God.