Three things weaken the strength of man:--Fear, travel, and sin. Fear,
as it is written (Ps. xxxviii. 10), "My heart palpitates, my strength
faileth me." Travel, as it is written (Ps. cii. 23), "He hath weakened
my strength in the way." ... Sin, as it is written (Ps. xxxi. 10), "My
strength faileth me, because of my iniquity."
THE TALMUD, _Gittin_, fol. 70, col 2.