Why I write textbooks

A student emails me:

Hey Professor Mankiw,

I hope you're having a good summer. I took your ec10 course this year and really enjoyed it, and I'm sure it helped me get my current summer consulting job.

My father, a physician, has no financial background. However, he borrowed my copy of Principles of Economics and has been unable to put it down. He's in the macro section and is fascinated by the monetary system. He really likes your book, to say the least.

Best,
[name withheld]

My life will have been well-lived if I can help a few more physicians understand the intricacies of fractional-reserve banking.