583. Performing a Labor Better or Worse Than Intended

Shabbos 1:12

If a person intended to perform a forbidden act of labor and he ended up doing so more effectively than he had planned, he is liable. If he ends up performing it less effectively than  intended, he is not liable. For example, if one intended to carry something hanging behind him and it swung to be front of him, he is liable because he ended up protecting the object more effectively than intended. But if he intended to carry something hanging in front of him and it swung around to be behind him, he is not liable because he carried the item less effectively than he had intended.

Shabbos 1:13

If a person wearing a belt carried something that is normally transported this way between his body and his garment, whether the item hung in front of him or swung behind him, he is liable because something carried in this manner commonly shifts around.