We consider the shift of charge-to-mass ratio for extremal black holes in the
context of effective field theory, motivated by the Weak Gravity Conjecture. We
constrain extremality corrections in different regimes subject to unitarity and
causality constraints. In the asymptotic IR, we demonstrate that for any
supersymmetric theory in flat space, and for all minimally coupled theories,
logarithmic running at one loop pushes the Wilson coefficient of certain
four-derivative operators to be larger at lower energies, guaranteeing the
existence of sufficiently large black holes with $Q>M$. We identify two
exceptional cases of nonsupersymmetric theories involving large numbers of
light states and Planck-scale nonminimal couplings, in which the sign of the
running is reversed, leading to black holes with negative corrections to $Q/M$
in the deep IR, but argue that these do not rule out extremal black holes as
the requisite charged states for the WGC. We separately show that causality and
unitarity imply that the leading threshold corrections to the effective action
from integrating out massive states, in any weakly coupled theory, can be
written as a sum of squares and is manifestly positive. Quite beautifully, the
shift in the extremal $Q/M$ ratio is directly proportional to the shift in the
on-shell action, guaranteeing that these threshold corrections push $Q>M$ in
compliance with the WGC. Our results apply for black holes with or without
dilatonic coupling and charged under any number of ${\rm U}(1)$s.