en to his introductory
paragraph as he opens up to us new "levels of energy" which are
usually "untapped":

[Footnote 48: James: _On Vital Reserves_.]

Every one knows what it is to start a piece of work, either
intellectual or muscular, feeling stale--or _cold_, as an
Adirondack guide once put it to me. And everybody knows what it
is to "warm up to his job." The process of warming up gets
particularly striking in the phenomenon known as the "second
wind." On usual occasions we make a practice of stopping an
occupation as soon as we meet the first effective layer (so to
call it) of fatigue. We have then walked, played or worked
"enough," so we desist. That amount of fatigue is an efficacious
obstruction on this side of which our usual life is cast. But if
an unusual necessity forces us to press onward, a surprising
thing occurs. The fatigue gets worse up to a certain critical
point, when gradually or suddenly it passes away, and we are
fresher than before. We have evidently tapped a level of new
energy, masked until then by the fatigue-obstacle usually obeyed.
There may be layer after layer of this experience. A third and
fourth "wind" may supervene. Mental activity shows the phenomenon
as well as physical, and in exceptional cases we
may find, beyond the very extremity of fatigue-distress, amounts
of ease and power that we never dreamed ourselves to own, sources
of strength habitually not taxed at all, because habitually we
never push through the obstruction, never pass those early
critical points.

Again Professor James says:

Of course there are limits; the trees don't grow into the sky.
But the plain fact remains that men the world over possess
amounts of resource which only very exceptional individuals push
to their extremes of use. But the very same individual, pushing
his energies to their extreme, may in a vast number of cases keep
the pace up day after day, and find no "reaction" of a bad sort,
so long as decent hygienic conditions are preserved. His more
active rate of energizing does not wreck him; for the organism
adapts itself, and as the rate of waste augments, augments
correspondingly the rate of repair.[49]

[Footnote 49: Ibid., pp. 6-7.]

Another psychologist, Boris Sidis, writes: "But a very small fraction
of the total amount of en