Ask a man what he want most in this life and you will get answers like riches, glory, soulmate, grandchildren, reputation, immaculate/good name and all sorts like that.
Humans tend not to know exactly what they want. We misinterpret our desire for riches as desire for money. We search for love when what we want is mate and convince love with marriage.
Man’s greatest desire is not materialistic, in fact, our greatest desire sounds impossible but everything we do is done so that we get the feeling of satisfying this desire. Our greatest desire is IMMORTALITY.
Humans are mortal being, all animals are mortal being, all plants are mortal. We will die someday, everyone we love will die, our pet will die, everything we know or love will die before us or after us. Imagine our sad and painful it is losing someone you lose, imagine our painful it is for your parents, spouse, children and friend when they lose you. It's painful and we don't want such, we run from it as much as we can.
Every action we take everyday is to ensure we don’t die and to ensure our loved ones don’t die. We are always telling death to wait and give us just a little more time. We eat because we want to live, we feed the children so that they can grow. We buy goods because we hope to use them. We go to school because we want a job and we want a job because we want to survive.
Other things that give us a sense of immortality are; children, surname, lineage, offspring, reputation, glory, success and assurance of the survival of future generations.
We protect our children in every way from every form of danger even if it is probably not life-threatening because we can’t bear losing them. We want a male child because we want them to bear our surname and represent the family in the future. We want grandchildren so that the lineage can live on.
We worry about climate change and other environmental threat because we don’t want to go into extinction. We promote advance in biology, Chemistry, Physics, astronomy and space travel to ensure the survival of our offspring. We want to make great discovery, invention, fame, power, contribution to the world, become a hero or whatever we think will make our name live on forever.
If you’ve ever had a child, I’m sure it is one of the happiest moment in your life and your parent’s life. It is your joy because it satisfies your deep inner desire for someone to take over the baton in this endless relay race of life.
There are thousands of religion in this world, but Abrahamic religion (Christianity, Islamic and Judaism) take over 50% of the world population and is one of the most powerful forces in this world. People believe in it not because there is proof that the God of Abraham is the only true God. They believe in it because it satisfies their most wanted desire, immortality in a place without pain nor sorrow. Abrahamic religion took it one step further by promising an eternity of pain and anguish if you don’t believe or if you break the law, there is no second chance to come to this world and redeem your soul.
Why has human come to believe soul or spirit exist? What ever else we want, we want it for eternity. I stand to be corrected, let me know your view in the comment.
While I'd like immortality I can not fool myself into the illusion of immortality you describe. Whatever you do in this life in the grand scheme of things it is meaningless and your legacy, no matter how big or important it is today, will be lost in time. I just want to enjoy life while it lasts, mortality be damned.
I admire that.