This most common of standing habits is both a backward and lateral mis-commitment of weight, resulting in a floor contact way back on the outer part of the heel.
A backward weight commitment resulting in floor contact being way back on the heels.
A backward weight commitment with a compensatory reaction that pulls us forward, resulting in floor contact being more on the balls of the feet.
A less-typical form of mis-commitment, but one we are all familiar with. We just don't do it as much as we do the other three. With feet spread wide apart, we direct our fall in-between the two feet. This literally pull us toward the empty space and results in floor contact being way on the inside of the feet.