When Lao Tzu left China, Guan Yi Tzu (关尹子) was the last person Lao Tzu talked to in China. He was the gate keeper that let Lao Tzu out of China.
Lie Yukou (列禦寇; 400 BCE) is considered the author of the Daoist book Lie Tzu, which uses his honorific name Lie Tzu (列子).
Lie Tzu studied archery. He shot many times, finally he got one on the target. He reported his archery situation to Guan Yi Tzu.
Guan Yi Tzu asked, “Do you know why you got that one on target?”
Lie Tzu said “Not yet.”
Lie Tzu kept practice. Three years later, he reported his archery situation to Guan Yi Tzu again.
Guan Yi Tzu asked again “Do you know why you got that one on target?”
Lie Tzu said, “I found out the cause this time”
Guan Yi Tzu said, “ Very good, you must remember the cause, managing a country and treating people have to be the same way.”
When we doing Tai Chi, we should not just mimic what the teacher does, we need to find out the cause for each movement. If you can understand that, then you can be one step further.