  We describe two puzzles that arise from a semiclassical treatment of
near-extremal black hole thermodynamics. Both puzzles are resolved by realizing
that quantum corrections become arbitrarily large at low temperatures, and we
explain how the spectrum and dynamics of near-extremal black holes are
modified. This analysis also implies that without low energy supersymmetry,
such as in the real world, extremal black holes at exactly zero temperature do
not exist since the classical picture breaks down completely. In the context of
supergravity the analysis is modified; supersymmetric extremal black holes do
exist and they are separated from the non-extremal spectrum by a gap power-law
suppressed in the entropy. This justifies black hole microstate counting
performed in the 90's using string theory.
