It's a great question. I ask that to myself almost all the time. I don't think the life's purpose has anything to do with success in the first place.
Its about being happy; being at peace with yourself. Money can't buy that; neither can success. It may please you momentarily, but it won't be long before the gloom sets in again.
One thing that i believe is the purpose is to live for the happiness of others. How often do we do something for others while we are engrossed in our own material pleasures? Well, you need to answer that to yourself!
We have to find a way to live for others. Have you ever tried helping a friend/ a complete stranger/ an elderly person/ a poor helpless person in need? Believe me, you! It will make your life worth living. There's a kick to that. Not that you are getting anything material out of it but it sure does put your mind at ease and peace.
I've found humanity in more animals than I did in humans and we are at the top of the food chain.
Christ, there must be a reason why humans evolved so much and other organisms didn't. Well if we did, how can we mess everything what we have created? Probably De-Evolution would be a better idea for the human race? Or who knows, if that's exactly where we are heading!!
So, start now! Lets HUMANIZE THE HUMANS and LIVE FOR OTHERS instead of ourself. Because that's our calling and that's our refuge from this unforgiving, sickening life that we have created for us.