He worked for IBM for many years, but don't let that fool you. The original version of this book has been influencing software designers and companies for 20 years, and he's not about to stop now. I thought you would never ask. For those techies among you, let me run down a few of Dr. Brooks' conclusions. A completed product requires about nine times as much effort as a program.
All programmers are optimists.
Small development teams are best - 10 people is optimum. What's more, he backs it up with the facts to prove it. In his updated 1995 notes, he points to Windows NT as an example of this. I can personally think of quite a few others. An essay that was published separately in 1986 is reprinted in this edition, along with a 1995 update.