In “The Man Who Mistook His Wife for a Hat: And Other Clinical Tales”, Oliver Sacks writes:

“A ‘phantom’, in the sense that neurologists use, is a persistent image or memory of part of the body, usually a limb, for months or years after its loss.

All amputees, and all who work with them, know that a phantom limb is essential if an artificial limb is to be used. Dr. Michael Kremer writes: ‘It’s value to the amputee is enormous. I am quite certain that no amputee with an artificial limb can walk on it satisfactorily until the body-image, in other words the phantom, is incorporated into it.’”

In this example, the lack of the limb is the constraint. The phantom limb could be seen as a curse to the amputee; however, that curse becomes a strength. The amputee can maximize the utility of the artificial limb if the phantom limb is present.