in some way, aversion
from the immutable good, and conversion to a mutable good, but not
always in the same way. Because, since the theological virtues have
God for their object, the sins which are contrary to them, such as
hatred of God, despair and unbelief, consist principally in aversion
from the immutable good; but, consequently, they imply conversion to
a mutable good, in so far as the soul that is a deserter from God,
must necessarily turn to other things. Other sins, however, consist
principally in conversion to a mutable good, and, consequently, in
aversion from the immutable good: because the fornicator intends, not
to depart from God, but to enjoy carnal pleasure, the result of which
is that he departs from God.

Reply Obj. 2: A thing may grow from a virtuous root in two ways:
first, directly and on the part of the virtue itself; even as an act
proceeds from a habit: and in this way no sin can grow from a
virtuous root, for in this sense Augustine declared (De Lib. Arb. ii,
18, 19) that "no man makes evil use of virtue." Secondly, a thing
proceeds from a virtue indirectly, or is occasioned by a virtue, and
in this way nothing hinders a sin proceeding from a virtue: thus
sometimes men pride themselves of their virtues, according to
Augustine (Ep. ccxi): "Pride lies in wait for good works that they
may die." In this way fear of God or horror of one's own sins may
lead to despair, in so far as man makes evil use of those good
things, by allowing them to be an occasion of despair.

Reply Obj. 3: The damned are outside the pale of hope on account of
the impossibility of returning to happiness: hence it is not imputed
to them that they hope not, but it is a part of their damnation. Even
so, it would be no sin for a wayfarer to despair of obtaining that
which he had no natural capacity for obtaining, or which was not due
to be obtained by him; for instance, if a physician were to despair
of healing some sick man, or if anyone were to despair of ever
becoming rich.
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SECOND ARTICLE [II-II, Q. 20, Art. 2]

Whether There Can Be Despair Without Unbelief?

Objection 1: It would seem that there can be no despair without
unbelief. For the certainty of hope is derived from faith; and so
long as the cause remains the effect is not done away. Therefore a
man cannot lose the certainty of hope, by despairing, unless his
faith be removed.

Obj. 2: Further, to prefer one's own guilt to God's mercy