"Never miss an opportunity to make others happy, even if you have to leave them alone in order to do it."
I used to honesty believe that I knew what was best for other people. If only they would do this or that; change in a specific way or reconsider the priorities in their lives, then they would feel better- and I would too. But I've learned to let people be and trust that they will know what they need to know when they need to know it, and not as the result of my prompting, or by my demand.
I mind my own business and allow others to do the same.