His investment strategy is based on the 'principle' that the stock market offers the best returns for long-term investors.
As 'a matter of principle', he would not accept the gift. [=he did not feel that it was right to accept the gift]
She refused 'on principle' [=because of her beliefs] to give toy guns to the children.
(..) I will do this. You have faith. I envy that. Justice, integrity, faith in humanity... nobody embodies those principles more than you. . And I know it must be hard for you to believe that you'll continue to embody those principles even after you watch me do this. (..)2016 TvShow: The Blacklist Title: Alexander Kirk (No. 14): Conclusion Season: 3 Episode 23