The mistress is not mentioned in this sonnet. Instead, the poet pens a violent diatribe against the sin of lust. The sonnet's angry attack on sexual pleasure stands between two rather innocuous sonnets addressed to the woman at the keyboard, and serves as a commentary on the morning following a night of pleasurable indulgences. The poet suffers a kind of panic in realizing how vulnerable he is to losing self-control to lascivious impulses. It is the paradox of having to fully let go in order to enjoy emotional release yet regretting the inescapable loss of control, the same control he was jealous of the mistress having over the "dead wood."
Although Sonnet 129 never directly refers to any character, it does indirectly express the poet's character in strongly marked antithesis, the excited impatience of lust contrasted with the revulsion that follows gratification: — "A bliss in proof and proved, a very woe; / Before, a joy proposed; behind, a dream." The poet often reverses the order of words to give greater impact to his antithesis and to deepen the impression of conflict, as in line 2: "Is lust in action; and till action, lust." Line 14 — "To shun the heaven that leads men to this hell" — completes the antagonistic imagery.
Sonnet 129 reveals a fundamental weakness in the poet's moral being. He asks why his heart should be moved by what he knows to be worthless, and yet, obviously bound by passion, he cannot escape his lust despite his better self. He endeavors to convince himself that the Dark Lady is better than he knows her to be.