This is a book that nourishes me. If you've never read it, it's about how we can learn to control our consciousness to be happier. The interesting thing about the flow state is that we are happy when we are deeply engaged in something that completely takes our attention so we can't think about or worry about anything else! That activity has to be challenging enough to keep us engaged, but not so challenging that we give up. That's my interpretation at the moment anyway. You can listen to Csikszentmihalyi on this TED talk.