Because tomorrow will always come, and the sun will rise with or without you
I haven't lived long, but what I have learned is that there will be moments when we cannot be anything but sad. Moments when there is no brighter side. So with every chance there is for happiness, in any form, big or small, always take it.
People base their lives around a schedule, long term or daily. Once you realize the most important day of your life — when it ends, is nowhere to be found on one.. all becomes irrelevant. Then the only thing left to "plan" is your happiness.