Although gravity sees to it that we fall, it is we ourselves that decide how we fall. We have always been in control of our falling.
By an act of consciousness that I call "committing body weight" we determine the trajectory of our falling. In effect, we steer our falling.
In the first year of life, we are extremely motivated to learn to sit and stand. It is a high priority. We experiment, and pay keen attention to our every movement.
The quickest path to learning to sit and stand - indeed, the ONLY way to do so at this young age - is through learning to fully capture the force of our falling and to transform it into the neuro-muscular activity that produces uprightness. Virtually all infants do this successfully. It is our human inheritance, having evolved over millions of years.