No one said that the prescription should be serious. The whole pill is never meant to bring you to utter seriousness as to what the purpose of life really is. You often encounter the term "a purpose-driven life" seriously pertaining to stuffs to attain happiness, a character of life in which there imagined to dwell the undying bliss of living. And then you go on to a strict regimen of following the prescription to happiness forgetting along the way the first and only essence of life and happiness which is already here and now.
Happiness is not a goal in the end of the line. It is not the last bang of the gong in an orchestral presentation. Not when you're finished licking your favorite icecream; not when you're done with your orgasm; not when your hated neighbor is already dead or your in-grown nails have been removed. Happiness is the music along the music itself rugged or clean, rough or smooth, annoying or cool. If happiness is found at the end, then all people should already be happy by now. But no, because happiness is not at the end of the tunnel. Happiness is along the tunnel.
The purpose of life is not to be serious at finding out what the purpose of life really is. It is to live at this moment. Do not desecrate this moment by imagining there should be another kind of moment. There is none. If you happen to find the purpose of life, what are you going to do with it? Parade it? Running around naked, shouting eureka? Looking down on people for not finding their happiness as you think you just did?
The "purpose of life" is just a trick of the mind; a poetic language to deceive self from feeling the presence; a pious statement which belies the present moment in exchange of still inexistent notions and expectations.