Anselm on Man's Inexcusable Inability

Anselm (1033-1109) has been dubbed "the second Augustine." The excerpt below is from his famous work, Cur Deus Homo (Latin for Why the God-Man?), which discusses the incarnation and atonement of Christ. You may read the entire work here. Throughout the book, Anselm converses with "Boso." I am not sure if "Boso" was a real person or just a literary device intended to give the book a more conversational tone.

CHAPTER XXIV.How, as long as man does not restore what he owes God, he cannot be happy, nor is he excused by want of power.
Anselm.. If a man is called unjust who does not pay his fellow-man a debt, much more is he unjust who does not restore what he owes God.
Boso. If he can pay and yet does not, he is certainly unjust. But if he be not able, wherein is he unjust?
Anselm.. Indeed, if the origin of his inability were not in himself, there might be some excuse for him. But if in this very impotence lies the fault, as it does not lessen the sin, neither does it excuse him from paying what is due. Suppose one should assign his slave a certain piece of work, and should command him not to throw himself into a ditch, which he points out to him and from which he could not extricate himself; and suppose that the slave, despising his master's command and warning, throws himself into the ditch before pointed out, so as to be utterly unable to accomplish the work assigned; think you that his inability will at all excuse him for not doing his appointed work?
Boso. By no means, but will rather increase his crime, since he brought his inability upon himself. For doubly has he sinned, in not doing what he was commanded to do and in doing what he was forewarned not to do.
Anselm.. Just so inexcusable is man, who has voluntarily brought upon himself a debt which he cannot pay, and by his own fault disabled himself, so that he can neither escape his previous obligation not to sin, nor pay the debt which be has incurred by sin. For his very inability is guilt, because he ought not to have it; nay, he ought to be free from it; for as it is a crime not to have what he ought, it is also a crime to have what he ought not. Therefore, as it is a crime in man not to have that power which he received to avoid sin, it is also a crime to have that inability by which he can neither do right and avoid sin, nor restore the debt which he owes on account of his sin. For it is by his own free action that he loses that power, and falls into this inability. For not to have the power which one ought to have, is the same thing as to have the inability which one ought not to have. Therefore man's inability to restore what he owes to God, an inability brought upon himself for that very purpose, does not excuse man from paying; for the result of sin cannot excuse the sin itself.

(Underlining has been added for emphasis)