Life's like a pair of shoes. You wear one that fits because it fits and you wear them as long as they are comfortable and as long as they fit. When your feet grow big you so away them and get a bigger pair because the earlier doesnt fit you anymore. The shoe here represents life as it is with the relationships it involves, the people that you interact therewith...so on and so forth. You've got to change them when they dont fit. Remember this quote:
"Asking what life means is like asking what carrots are. All we know is that they are carrots and thats all."