"Time: that is the key. Forget dollars, cowrie shells or gold. The true measure of something's worth is the hours it takes to acquire it."
- Matt Ridley, in The Rational Optimist: How Prosperity Evolves
This quote is from a section of the book in which he discusses how much more an hour's worth of work buys the average worker now than in pre-industrial times.
(I've written about the book before, in the context of my musings about the different types of success.)