Surely it is the maxim of loving-kindness: Do not unto others that you would not have them do unto you.
A gentleman would be ashamed should his deeds not match his words.
A gentleman does not promote a man on account of what he says; nor does he reject sayings, because the speaker is what he is.
A truly great man never puts away the simplicity of a child.
Silence is a true friend who never betrays.
There is one word which may serve as a rule of practice for all one's life -reciprocity.