Stance training is the most essential in any kung fu regimen. Proper balance from stance is required to execute techniques in kung fu.
In the case of executing sow chui, a large looping roundhouse hook punch, requires a strong balance of stances. Sow chui is a technique which gathers a lot of energy during the swinging execution. In addition, the power gathered from the whipping of the hip/waist gives the techniques a devastating blow to the target upon impact, similar to swinging a sledgehammer to break concrete blocks, mortar, etc. If the balance of the person executing sow chui is not strong or rooted to the ground, the person will fall during execution.