The same Greek word translated as "life" in this verse is translated as "soul" in the next verse. This creates a clear paradox because Jesus clearly meant the same thing because he used the same word in the same context. This concept is discussed in detail in this article about this Greek word. 

We also see the opposite problem where two different Greek words are translated as the same English word. The word "save" here is a more common Greek word, while the one in the next verse is only used in that verse and its parallels in Mark and Luke. The key opposites here are "save" and "lose," which, in English, are very general words,  but in Greek, the words used have a meaning more directly related to what is translated as "life" and "soul." They have the sense of "rescue" and "kill."