1. Time waits for no one.
If you are upset, angry or sad, feel it. Go through it. All of it. Each and every bit of it. But do not spend most of your precious time in that rut for long. Pick yourself and try again or do something completely different. Change strategy.
This does not apply to grief or loss because there is nothing that anyone can say to make you feel understood or comforted. Time in this case, heals wounds.