– Navajo proverb
I love that this is a proverb whose interpretation isn't especially obvious (which means it's open to many!).
My interpretation: don't waste your time on those who refuse to acknowledge the truth they observe. While this may seem pessimistic or defeatist, sometimes I think energies are better spent working with people who are open to whatever it is you're working on. All we can really do about the naysayers and hard-heads is hope and wait for them to soften in their own time. Their time, not ours – we've got things to get done!