I'm not a big fan of the phase "work-life balance." It implies that the two concepts (work and life) take up equal space, which is not the case for most people.
With 168 hours a week, if you sleep 8 per night (56 per week) that leaves 112 for other things. You'd need to be working 56 hours per week for work and the rest of life to be truly "balanced." Most people -- even those working full time -- don't come close. We work far less than we think we do. I like the "fit metaphor" from consultant Cali Yost, because the exact proportions aren't specified.