天下同归而殊途，一致而百虑 All under heaven come to the same end by different roads. There is one outcome and a hundred considerations. (Book of Changes)
殊途同归 Different roads, the same destination. The Handian dictionary traces it to this line. Different methods reach the same result.
万变不离其宗 Ten thousand changes, never leaving the origin. However the form changes, the essence stays the same.