  I re-examined the notion of the thermodynamic force constructed from the
first law of black hole thermodynamics. In general relativity, the value of the
charge (or angular momentum) at which the thermodynamic force equals the
conjectured maximum force $F=1/4$ is found to correspond to $Q^2/M^2=8/9$
(respectively, $a^2/M^2=8/9$), which is known in the literature to exhibit some
special properties. This provides a possible characterization of
near-extremality. In addition, taking the maximum force conjecture seriously
amounts to introducing a pressure term in the first law of black hole
thermodynamics. This resolves the factor of two problem between the proposed
maximum value $F=1/4$ and the thermodynamic force of Schwarzschild spacetime
$F=1/2$. Surprisingly it also provides another indication for the instability
of the inner horizon. For a Schwarzschild black hole, under some reasonable
assumptions, this pressure can be interpreted as being induced by the quantum
fluctuation of the horizon position, effectively giving rise to a diffused
"shell" of characteristic width $\sqrt{M}$. The maximum force can therefore, in
some contexts, be associated with inherently quantum phenomena. Some
implications are discussed as more questions are raised.
