We establish the physical origins of chemical transferability from the perspective of the nearsightedness of electronic matter. To do this, we explicitly evaluate the response of electron density to a change in the system, at constant chemical potential, by computing the softness kernel,
. The softness kernel is nearsighted, indicating that under constant-chemical-potential conditions like dilute solutions changing the composition of the molecule at � has only local effects and does not have any significant impact on the reactivity at positions far away from point �. This locality principle elucidates the transferability of functional groups in chemistry.