That depends on intent hellish. I don't think cheating is about failure, it's about not trying. If the sub agrees to accept or try a task but knows he/she really didn't intend to try, then he/she cheats themself and their dom, regardless of the eventual confession.
Anticipation of you completing an assignment is part and parcel of a Dom/me's enjoyment. Continued failure to complete such tasks cheats the Dom/me who comes to expect nothing more than the upcoming confession.