Carlson was not a particularly happy Angel. You see, he wasn’t allowed to live in Heaven. He was a Guardian Angel, which meant that he had to hang around on Earth, taking care of his Client, Bob.
Now, Guardian Angel duty was about the most difficult job an Angel could have, even under the best of circumstances. Angels couldn’t change what their Clients said or did; they could only try to protect them from accidents. Or, more commonly, from the consequences of their actions.