Most of us want better posture but how to achieve this is the question. We think that if we look at a diagram of what posture is supposed to be that we can press ourselves into that mold. Western disciplines only understand force and overlook subtlety, so if we want to achieve good posture we try to forcefully hold ourselves in positions that we think exhibit good posture, but through our naive understanding of how our muscles and nervous systems work, we are not only deceiving ourselves but probably doing ourselves a disservice in the process.
When we use force to hold ourselves in this or that posture we undoubtedly enlist a whole range of muscles to do so, and many of those muscles are not really fit for the job. This happens because we do not understand the deeper mechanics of the body, what it takes to sit, stand, and move around with the near effortless elegance that we are designed for by nature. Western disciplines, physical therapy, Pilates, almost all common gym exercises, and most of the yoga we see in the west only understand the overt gross over simplification of physical movements and alignment but do not understand the covert subtly that is necessary to actually do these things with any grace. This is not necessarily true of eastern disciplines, at least some of them have a refined attention to movement and sensation.
In traditional Japanese swordsmanship there is the understanding that if a person goes into a battle and becomes fatigued they may quickly tire and be killed. Anyone who practices a fighting art or who has been in a fight knows that even 10 minutes is a very long time to be in a physical conflict. In order to not become fatigued the swordsman must not use any unnecessary force or strength and use only what is necessary. Many martial arts revolve around this idea. Just as the swordsman understands that unnecessary force leads to fatigue, we must also understand that walking around holding our shoulders back, sucking in our gut and trying to tuck our pelvis this way or that will result in fatigue, because we are using muscles that are designed to be at rest with not performing activities like running, climbing, or defending ourselves.
If posture and movement are not optimal, we need to address the restrictions that are causing problems, we need to get support for structures that are not stacked well in gravity, and most importantly, we need to learn to participate in posture and movement in a better way. There is an innate wisdom in the body, and when we try to control it with our ordinary minds, we overpower it with our limited understanding. If we can learn to let up the habitual tendency to control everything it can eventually start expressing itself and we can start to move with greater freedom. This exploration of the innate wisdom of the body will lead to an inner balance and a greater mastery of movement as well as posture. This idea can be boiled down to just trying to relax while we do things. A master does not use force, but rather skill and understanding. We could all work toward trying to master being embodied creatures.