When you work more than 40 hours per week, you're borrowing time from your future self. However, the interest rates are very high, and so usually it doesn't make sense to borrow this time.
This is so so true ... I've been doing 4.5-5.5 hour nights (sleep) for years and very recently have started to see the effects in aging ... greying and balding at a much earlier age than I anticipated (for example). I've made my peace with it now, but I can't help but wonder how much I would have cheated aging if I had been sleeping 7/8 hours a night instead.
More scary is how much of the detrimental effect of lack of sleep I am yet to encounter.
