Tim O'Reilly - Just don't run out of gas

To me, the following analogy by Tim O'Reilly seems to be referring to 'money during retirement'. When thinking about how much is enough, the metaphor of 'gas for the road trip' seems very apt.

Tim O'Reilly: It was at this time that I formulated an image that I've used many times since: profit in a business is like gas in a car. You don't want to run out of gas, but neither do you want to think that your road trip is a tour of gas stations.

Replace "profit in a business" with "money during retirement." I have referred to the quote before, but I read it today in Tim's Google+ post, where he muses about the legacy that Steve Jobs left behind, and the wisdom of Tim's analogy hit me afresh.