If you can find a perfectly flat, level surface, and walk across it in as straight a line as you can manage, each step may look very much like the last one, but they will not be identical, in fact no two will be exactly the same.
This will be more true when walking across a surface with slight variations, and still more true when walking a rough trail. Each step is a unique action designed to keep us moving generally in the chosen direction, and while we may pay conscious attention to the process, and consciously choose among various options (placing your foot to the left or the right of a rock or on top of it), the calculations involved in determining the fine adjustments all happen unconsciously, and are already being executed by our muscles by the time we become aware of them, if we do at all.
In working one's way through a dense maze, say through a forest thick with trees, both standing and fallen, and underbrush, the path one takes becomes more complex, and far more interesting, engaging the conscious mind to a greater degree. And while the overall motion can no longer be described adequately in terms of steps, let's continue to concentrate on foot placement.
At various times you will find yourself standing with your toes turned inward, at other times your feet will be parallel, and still other times they will be spread to varying degrees, at every conceivable angle the range of motion of your joints will allow.
So it is with practice. There is no one right way to stand. Rather, one's feet and legs should become accustomed to and learn to support every variation on the theme. Classic stances represent extreme positions, but are hardly ever used in their pure form because each has its own instability. Instead use them as starting and ending positions, and concentrate on making smooth transitions between them.