> Barons of the Sky is a nice history of the early days of the aerospace industry, and it shows that in the early days, everyone was a hobbyist. Unlike other hobbies, like writing computer games for fun, this was a high-stakes pursuit. Good amateur plane designers made the front page when they set records, the bad ones made the obituary page instead.

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> And since the tweet mentioned rockets, it would be wrong to ignore one of the founders of the Jet Propulsion Laboratory, Jack Parsons, who helped invent modern rocketry, founded a cult, got expelled from Caltech for a bit of both, and died from a rocket explosion at his home lab.

> Hedge funds do this, too. At a typical stock-picking hedge fund, the decisive interview questions are about what stocks you like and which ones you hate. Some anecdotes:

> Lars Kroijer, a young MBA, scored an interview with a very good hedge fund in the 90s. He describes the interview in his memoir. The manager asked him for stock picks. He said the market was inefficient, so the manager asked him to leave. Ouch! Lars straightened himself out and went on to run a successful fund, then retired at the right time. At another fund I’ve heard about, the head of research liked to poll the interns and ask them if they thought the market was efficient. If the answer was yes, he said, they were fired effective immediately. Fortunately, in an efficient market it should be effortless to get an equally attractive job elsewhere. I’ve bombed at least one interview by not having any good trading pitches handy. (In fairness to me, it was a fund using a strategy I hadn’t ever worked on. In fairness to them, I knew this.)

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> As many people point out, the norm in favor of side projects is unfair to anyone with limited free time. What they don’t add is that this is a progressive tax: there’s a positive correlation between educational attainment and hours worked per week, as well as between income and hours worked per week. This was not always the case; “The idle rich” used to be a statistically accurate observation, but now the rich work longer hours and have less leisure time than average. But the average American watches four and a half hours of TV per day. If your work happens to be fun, you can devote that leisure time to side projects. If your work is boring, you probably shouldn’t complain that people who like their craft more than you and devote more effort to it are rewarded.

> (As a friend put it a few years ago, when such pop culture references were relevant, “If you know what a ‘Khaleesi’ is, you had time for side projects.”)