But instead you buy a table from Apple and it's only compatible with chairs from Apple. So you can't pay your local carpenter for repairs or better chairs.

Anyway, the big companies have long since realised it's more lucrative to stop selling the furniture and rent it out instead.

What do you build?

1. Internet has made distribution frictionless. So unlike giving out Uber trips, giving out code costs you nothing.

2. You have a real job. The "80% time" for which you're paid subsidizes the self-promotional work you do for free, and let's not kid ourselves: most of us write open-source not out of altruism but for the recognition.

3. Software is immediately useful. Lawyering is a lot like programming in that both involve putting pen to paper in just the right way. But pro bono legal work is a lot more painful than whipping up some code. Lawyers have to deal with people and all their bs.

4. Software is easy. I don't know why but the return on capital blows away the return on labor. Whereas Microsoft may have once derived most of their profit from software, they've now come around to the rest of the tech industry which is selling hardware and compute -- the software that comes with it is included.