Which book? The Mythical Man-Month?
I guess I can see how it might depress some people, because what he wrote about in 1975 is just as true today, which of course means that management hasn't improved even a little in that time. However, if that's your only take away, you should read it again.
The lesson I learned - and in many cases, I don't think it's what Brooks intended, but it was what I learned anyway - is this: recognize that, in many senses, software development is inherently unmanageable, trying to manage it is only making things worse, and that you should stop trying to do it. Your best efforts should be spent on the people, not the development process.
Staggering amount of time's been wasted on "standup meetings" (all hands status report) and "estimates" (the worlds slowest random number generator), and all of the other stupid management decisions that live around that.