The Gemara asks why does the Mishna relate both cases where a man may nullify a Get he sent to his wife, by directly telling his wife that the Get that he sent with a messenger is null and void, or also by sending another messenger to his wife telling her the Get is null and void. The Gemara explains that in the first case there is more of a likelihood that he really means to nullify the Get because he went through the effort himself to tell her it is void. He would not do that just to cause her pain. However, in the second case where he is not expending any effort, there is a greater likelihood that he means just to cause his wife pain and indeed he really wants the Get to work. Therefore, it is necessary for the Mishna to tell us that even if he sent another messenger to tell his wife the Get is invalid, it really is invalid.
This can be a very useful tool in combating the Yetzer Hara. When someone has a desire to do something wrong, he can utilize his natural laziness to not bother to do that wrong thing. This is one of the understandings of the concept of serving G-d "B'chol levavcha" with both your Yetzer Harah and your Yetzer Hatov.