this is a hugely challenged and debated topic, and I would be naive to suggest that I know answer to this, except 42 maybe. Anyways, I read a book by Frankl, obviously called "men's search for meaning of life" and I was influenced by it in more than one way. Without garbing it under subjectivity of my understanding, I am will reproduce as is the thought process in the book .

First it talks about meaning of life, and says is there necessarily a meaning of life. Or rather it is a continum of meanings. Or in different words meaning of life is responding to questions and challenges in everyday life. Each individual, in each different context and situation can give different meaning to life by how he responds to what life puts in front of him. And it is that response or decision that provides meaning to life.

He then goes on to argue that life finds meaning in any circumstance however bleak it is. His examples come from concentration camps where meaning of life was as simple as when to eat my only piece of bread.

This relates back to what Geeta (Indian book about Karma) says. It talks about do what you can do best, be aware that you do not choose the circumstance but you do choose what you have to do. And it your karma that will define you. Or in other words meaning of your life...