Hard chi kung hits onto the target, soft chi kung hits into the target. A soft chi blow penetrates into the body cavity damaging the mostly liquid internal organs. A hard blow seeks to break the outside body defenses of muscle and bone to cause injury that disables from the outside in. A soft blow shuts down the internal organs that drive the body by sending shock waves of chi through the outer body defenses and into the vital organs, thus disabling from the inside out. You get hit with a hard blow it hurts where it hit you.
Soft training focuses on teaching deeper and deeper levels of relaxation.
The saying goes that the first level of relaxation is to feel your muscles and tendons relax. This is as far as the average person ever goes. The second level of relaxation is where you can feel your skin and hair relax. The third level is where you can feel your internal organs relax. The forth level is where you can feel the marrow of your bones relax.