Sometimes it's just not there.
It took, inexplicably, four tries to finish the toe for this sock. This is not my first sock, by any means. (Ok, it was mostly done in public while trying to do something else at the same time.) I messed up stitch counts, I messed up row counts, I decreased too quickly or too slowly. Argh.
I got it done, though, after I'd ripped it back four times.
I guess it's a different kind of mojo: the need to get it right. Would it have fit and worn ok if I'd left it with any of the mistakes I'd made? No question. Would anyone else have known? Of course not. But I'd have known and it would have annoyed me.