Most people don't understand nihilism. They think that it means you are negative and dark. This is not true. Simply speaking, nihilism represents the belief that life has no inherent purpose, value, or meaning. Inherent is the operative word. Because life has no meaning in and of itself, the meaning your life has is the meaning you give it. There is a lot of hope in that. Meaning does not come from outside yourself, it is not dependent on a god or other people. This is the only life we have and it is precious because of that. I suppose I consider myself an existential nihilist. I do believe that existence precedes essence and that we are what we do. (To oversimplify.) I believe in life-driven purpose, as opposed to a "purpose-driven life" (an emphasis on god). Life can end in a second. Best to enjoy each moment we have; one day we will cease to exist - forever. We are but specks of dust. That's why it's pointless to beat ourselves up for mistakes we have made. They really don't matter. All we can do is learn from those mistakes and move on. We are the sum total of our experiences, good and bad. So there is no need for regret.
Memento Mori "Remember thy death". Essentially, it is a reminder that we are mortal and that we should not make a big deal out of anything, even our accomplishments.
(Because I can laugh at myself. "Rule 62": Don't take yourself so seriously.)
“A universe without purpose should neither depress us nor suggest that our lives are purposeless. Through an awe-inspiring cosmic history we find ourselves on this remote planet in a remote corner of the universe, endowed with intelligence and self- awareness. We should not despair, but should humbly rejoice in making the most of these gifts, and celebrate our brief moment in the sun.”