There’s a little secret in life drawing that not many artists know about. If you know about it you’re already using it, if not, you will start after reading this article.
It can be our little secret.
Here it is: If you want your figure to have a natural look, use convex (outy lines) and not concave (inny lines).
Why? Everything alive starts as a molecule and begins to grow. Growing is an outward motion. As things grow, they begin to take on a bulge toward the outwards or convex.
(I think my stomach adopted this law too personally.)