Actually, it's not the lips but rather, the tongue. This simple human organ, once it spits the words out, it cannot take them back.
Hearsay claim that since the day of its creation (the tongue), it has always been thriving (all the time) to acquire the capacity of taking words back to where they came from, but nonetheless, failed.
On the other hand therefore, it remains to be the most difficult organ human beings can tame