From the Shirtpunch.com's interview with the artist:
"Question: What inspired this design?
Answer: The idea that we all have 2 sides to us. Hell man, some have 3 or 4. I got a cousin who has an entire cellblock wortha sides to him ! The point? To be a puppet and struggle with the fact that your nothing without your other half. This is the plight of the Incredible Frog. Buy the shirt and support The Lumberjack Thesis Committee."