The meaning of “Si-En” is „four-grace”. They are, the grace given by Heaven and Earth, the grace given by the Emperor, the grace given by one’s parents, and the grace given by one’s teacher. These are the grace one must remember and try to repay.
“San-You’, are the three haves. They are the ones who have compassion, the ones who have wisdom and the ones who have special connections (to us). These are the ones we need to be close with.