Here is an excellent Youtube video from The Wooded Beardsman site that explains how hard it is to live of the land for long periods of time. I liked how he explained how the Naked and Afraid survivalist were only enduring without food instead of thriving off the land.
You must constantly be on the lookout for food and water to replace lost calories so that the body can function properly and allow you to make smarter decisions in your survival situation.
Stay Prepared! Stay Alive!