The point of life is to have fun and meet people.
Optimism helps that.
A man becomes and remains optimistic by loving the people and experiences he has, learning from but not comparing anything to the people and experiences from the past, and not worrying about the people and experiences of the future.
The present masters most because it is here, and it is the only thing possible to experience. The past was there only to teach us, and no one knows what the future holds.
The future will be best if a man simply does his best, acts genuinely, and is receptive to others.
Enjoy the present. It makes up the entirety of your life.