I can often find serenity in accepting at and in the moment but not accepting permanence. As you say somewhere later in the essay, it's a balancing act. I think you'll appreciate my post on acceptance here: https://medium.com/promptly-written/spiritual-prompts-for-the-week-of-june-12th-18th-86877724cd6b It touches upon many themes you speak of, including my views on "it is what it is."