I disagree. He accepted the task, so he's responsible for finishing it, one way or another. Suppose you hired a handy person to do this, and they got to this point and gave up. You'd be pretty upset with them for wrecking your wall, right? Even if they didn't demand payment, you'd probably expect them to at least put it back in order. This situation is a great illustration of why we need to be careful about committing to take, but is also a great chance to learn to do the right thing, even if it's difficult or expensive.