The meaning of a question, and what counts as an answer, depend on the theoretical perspective you approach it from. I loved reading "Zen and the art of motorcycle maintenance". What he says is important. But he's not tackling this question from an economist's perspective.

To us economists, it's a puzzle why anyone would fix his own car. Not a very deep or insoluble puzzle, but still a puzzle that needs answering. Because what we teach in ECON1000 is that economies of scale (Adam Smith) and comparative advantage (David Ricardo) motivate specialisation and trade. I should stick to economics, and pay someone else to fix my cars. But I don't. Usually I fix my own cars myself. Why?

1. Because I enjoy doing it. In simplest micro models of the supply of labour (which is just 24 hours minus the demand for leisure) there are two ways to spend your time: working; and leisure. Leisure gives you more direct utility than working, but working gives you income, which you can use to buy things, which gives you utility indirectly.

But there are many different kinds of "work", and many different kinds of "leisure", and each of those many ways of spending your time gives you different amounts of direct utility. And some "work", like fixing your own car, produces goods (a fixed car) rather than money, and (for some people) is more enjoyable than their regular work (or less unenjoyable), and as enjoyable as some forms of leisure. All this gets ignored in simple models of specialisation and trade.

2. To avoid taxes. Suppose that both I and the mechanic face a 50% marginal tax rate. (It keeps the math simple, and is also roughly correct, or even an underestimate, if you add sales taxes to income taxes.) I could teach his kid economics, for cash, and he could fix my car, for cash. Suppose I can teach twice as much economics per hour as he can. Suppose he can fix twice as many cars per hour as I can. Even though I have a 4:1 comparative advantage over him in teaching economics (and he has a 4:1 comparative advantage over me in fixing cars), the 50% tax rate on each of those two trades means we will be indifferent between trading or not trading. Each of us has to earn $400 gross to give the other one $100 net. In a monetary exchange economy, a 50% tax rate on cash income becomes the equivalent of a 75% tax rate on barter, because there are two trades that get taxed (economics for cash, cash for car fixing), and not just one barter trade (economics for car fixing). (I wonder; do microeconomists, with their tendency to use formal models of barter exchange, recognise this point?)

3. Moral hazard/asymmetric information. (These are really the same, because if there were symmetric information, so you knew everything the mechanic knows, you would know if he were slacking off and doing a shoddy job because it's not his car.) My experience suggests that the biggest problem here is not mechanics doing too little, but too much -- fixing things that don't need fixing? I think that's the main fear of people who don't understand how cars work. Because you can usually tell if something hasn't been fixed that needs fixing; but you can't tell if something's been fixed that didn't need fixing.

4. Monopoly power. The perfectly elastic demand curves facing perfectly competitive firms are a simplification. Most sellers face a downward-sloping demand curve, so price above marginal cost. This means that the quantity of trades that take place is less than socially optimal. In other words, under monopoly, there is less trade in car-fixing and more people fix their own cars. Some potentially mutually advantageous trades, motivated by economies of scale and comparative advantage, are not made. It would cost the mechanic less to fix my car than it costs me to fix it, but i do it myself because he charges me a price above his marginal cost.

5. What else have I missed?

6. Update: Transportation costs. I shouldn't have forgotten that transport costs nearly always limit the gains form trade. "The division of labour is limited by the extent of the market". Getting my car to the mechanic (walking back), and getting it back (walking to the garage) are a major cost. Plus, He fixes the car when he has time; I have to book it in. I can fix it when I don't need the car as much.

And a few anecdotes, that don't really belong in this post, but I can't resist telling them.

A1. The dealer quoted my $80 for a new passenger side window switch. This is a very simple 3-position rocker switch. A generic version would probably costs less than $10 at an electronics store, but wouldn't fit the MX6's door and connector. So I spent an hour taking the tiny switch apart, cleaning the contacts, and putting it back together. Why is the cost so high? Partly it's the cost of maintaining inventory of a very large number of very specialised parts. But I read you can buy the switches for around $20 on Ebay (I couldn't be bothered with the hassle of Ebay), and the Ebay seller must also have similar inventory costs. It must be monopoly power. If car manufacturers could precommit to keeping parts prices reasonable, and if buyers paid attention to future parts prices when buying a new car, competition between car manufacturers would probably keep parts prices lower. But neither of those two conditions seem likely to be fulfilled.

A2. There are significant interprovincial trade barriers to buying a used car. I live in Quebec. If I buy a used car that's already registered in Quebec I don't need a safety check. But I bought an Ontario-registered car, and the safety check at one of a few licensed garages was mandatory. It cost $80, which is not unreasonable. The trouble is, when your car goes in for the safety check and they find anything major wrong (nail in tire in my case!) you are not allowed to drive the car away from the garage doing the check. If they find anything minor wrong (spare tire not anchored, battery not anchored, one slightly worn ball joint, one sticking strut mount bearing) you have 48 hours to get it fixed or you can't drive the car. I could have fixed it all myself, but maybe not in 48 hours, over a weekend, so they had me over a barrel. I paid them to fix it.

A3. I used to fix cars as a kid. Then I got busy, and cars got complicated, and I stopped. I started again because computers have made it easier to fix your own car again. First, the car's own computer can often tell you what's wrong (you need to invest in a $100 code reader to diagnose a check engine light, or just use a bent paper clip in the case of a pre-1995 car). Second, because the internet has made it much easier to compare notes with other people fixing their Mazda MX6. Car forums (linking my two internet worlds) contain a wealth of information and advice. They are like blogs, but different.