People know what they want or need in life. We know that we should be healthy. We know that we want to be good parents, friends, etc. We know that we should be our best. We all have concepts of what we should, need, or want to be - but the details are left out.
Ask 10 people what it means to be healthy. You'll probably get 10 different answers. But isn't that up to science? Why is it a matter of opinion?
Ask parents what it means to parent well. Everyone has different ideas for that concept.
What about being your best? The world wants to label you many things. You might even have labels for yourself. Who are you at your best? Will you ever reach "your best" or are you already there?
Do you see? I think life is about answering these questions. If you view life as constantly looking for answers to these concepts, then it's also a wonder where these ideas came from in the first place.
Everybody's different, but no matter what, we're all living life for the sake of figuring ourselves out. The cool part is that it requires interaction with one another, and that's really one of the best parts about life.