"The next piece is the upper and lower halves of your foundation. In Chen Taiji, you're missing something if your legs aren't sore. The feet and legs are the base of your or your opponent's structure. A building falls without a strong structure (legs) or with a misalignment of feet and legs."

Sifu's saying that goes with this principle was, "There are no secrets to Chen's Taiji, there is only practice." He would then tell the story about how Chen Fa-ko became Grandmaster. He practiced at night while everyone else slept. 

The gondola effect is building up leg strength by pushing into the ground. The feet and legs must be in the correct positions and move in coordination. In building the foundation, it's essential to practice smart. Movement must be slow, relaxed, and accurate to avoid injury.