Walking is odd. Don't put your foot down next time you are walking along, you don't just stop mid-step, you fall flat on your face. Walking is a controlled fall. I am learning to unicycle, its an ongoing thing, but sort of similar to walking. If you stay upright, when you pedal the wheel flies out from under you and you wind up lying on your back, cursing at the tree branches. If you lean to far forward without pedaling to compensate you get a noseful of dirt that reminds you of how moles live. So the secret is to lean forward just enough and to catch yourself by pedaling. Its tough.