Reminds me a lot of the teachings of Ajahn Brahm, of the Buddhist Society of Western Australia - the only difference being, life according to Buddhism, isn’t too short - it’s way, way too long: you’ve already died thousands of times & will continue to live & die again & again & again. Aside from that it’s basically the same - let go of useless striving, work on things you can control, starting by learning to control yourself, & foster compassion & loving kindness in your heart. Examine your immediate sources of pain & disappointment, find the causes & work on those (also kind of GTD-ish there), and whilst you accept that there’ll always be some kind of disappointment looming, you can gain happiness by living in the here & now. As Leonard Cohen says “There’s a crack in everything - that’s how the light gets in.”