The way the result works is that if you are a meter underground, it is equivalent to standing on top of a sphere with the top meter of mass removed. Or equival

The way the result works is that if you are a meter underground, it is equivalent to standing on top of a sphere with the top meter of mass removed. Or equivalently, if you are inside a shell (sphere outside, hollow sphere inside) then the gravitational effect is zero. This can be explained by analogy with light which also follows the inverse square law--changing your position inside a hollow sphere does not change the fact that you see the sphere all around you. Same reason that there is no electrical field inside a hollow conductive object.