The answer to that question is found in the performance of Mr. Cusack. He not only marches to a different drummer, he cranks the volume up to 11 so others may hear the beat. Because of Mr. Cusack's disarming self-deprecation, the convention works, giving us a humorous albeit shallow insight into a male psyche. The filmmakers have also been able to entice a number of recognizable names to fill the supporting roles. Rob's stunted development, preventing him from becoming a mature adult, is at the root of all his problems.
Growth is a sign of life.
As individuals full of life, we should always be seeking ways to grow and further ourselves. This would naturally include ways in which to grow spiritually. When we consider the alternative, growing up sounds downright appealing.