Another theory is that dreams typically reflect our emotions. During the day, our brains are working hard to make connections to achieve certain functions. When posed with a tough math problem, your brain is incredibly focused on that one thing. And the brain doesn't only serve mental functions. If you're building a bench, your brain is focused on making the right connections to allow your hands to work in concert with a saw and some wood to make an exact cut. The same goes for simple tasks like hitting a nail with a hammer. Have you ever lost focus and smashed your finger because your mind was elsewhere?