A while ago I read 'The subtle art of not giving a fuck' by Mark Manson. Nice book and nicely written as well, but no real eye-openers for me. Came to the conclusion that I could have written it myself. With that I mean that for a very long time already I followed the principles of what he describes.
Let go of things you can not influence yourself. Concentrate only on things you can get/have control over and are able to influence.
That is plain, simple and very true, I think. Somehow it would be good to have a reminder of some kind. A trigger that rings a bell, just to remind me of this.