Agree and add that it is also possible to have a 'principle' that commitment to a monogamous relationship is something that you do at times but that it is a big step that really means something in relationships that takes time and a particularly special connection. When things must be earned we experience them as so much more valuable.

A caveat is that principles, particularly more complicated principles, should never be lived (or signalled) in a way that is at all wishy-washy.