“Don’t lament this and don’t get agitated.” Marcus Aurelius, Meditations.
Save your energy for living in the present. Don’t allow emotions about things that have already happened to get the better of you: endless rumination about ‘if only’ will make those emotions resurface and feel almost as powerful as when they first occurred. In a similar vein, when faced with challenges in the future – actual or probable – allow your logical-thinking brain to come up with contingency plans. You’ll cope. You’ll be OK.