It is difficult to live in and enjoy the moment when you are thinking about the past or worrying about the future. You cannot change your past, but you can ruin the present by worrying about your future. Learn from the past, plan for the future. The more you live in and enjoy the present moment, the happier you will be.
All you will have is the present. Waste no energy crying over yesterday or dreaming of tomorrow. Nostalgia is fatiguing and destructive, it is the vice of the expatriate. You must put down roots as if they were forever, you must have a sense of permanence.