My question is simply an extension of this SE post; I don't understand why $q'+q''=0$ (both charges of hypothetical construct) for the sphere to be neutral.
I'm trying to find a parallel between the following two cases:
Point charge ($q$), and a conducting sphere.
Point charge ($q$), an image charge $q'$ and another charge $q''$ (to get the desired potential on the spherical surface of radius $R$, centered at $q''$
Please help me understand this better. Thank you!