When you are walking correctly the upper body leads the way forward through space and the psoas muscle catches you over and over again to prevent you from falling. As the trunk makes its way forward there will be a moment when the brain senses that the body is about to fall. At this exact instant the brain, through the workings of the nervous system, tells the psoas muscle (an a host of others) to bring a leg forward to prevent the impending crash.
This interaction between the brain, nerves and the psoas muscle is hopefully happening 10,000 times a day as you proceed through life. Unfortunately, from our perspective at CoreWalking, very few people are using the psoas muscle to walk. Instead we find that most people avoid the movement into the forward plane and instead drag there trunk forward in search of their legs.
Walking is a sort of falling and catching ourselves over and over again through the work of the psoas muscle. Be willing to go forward.