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.
If you do not enjoy a moment, you lose it forever. If you enjoy it, it is yours forever.
Dwelling on the past and worrying about the future will only rob you of the present's joy.