万变不离其宗
cling to one's original purpose or position despite a myriad changes; the method may vary but the principle remains the same; use ten thousand guises to serve a single purpose
e.g. 这号人的表现形形色色，但万变不离其宗，目的都是不劳而获。
Although people of this type may vary one from another in appearance, there is one thing about them which essentially remains the same, namely, they all want to profit by other people's toil.
