I was 15 when I first noticed something that took me 50 years to fully understand. My older brother, then about 25, was a young physician working through his fellowship on a stipend that barely covered his own expenses. A few times a week, we would join one of his friends, also a doctor, for breakfast. The friend had skipped the fellowship route and gone straight into private practice, earning something like three times what my brother made. And yet, when the bill arrived, it was almost always my brother who reached for it first.

I noticed it. I did not understand it. At 15, you file such things away without a theory to explain them, and I filed this one away for half a century.