In this classic book on the software development process, Fred Brooks demolishes several persistent myths. They never quite go away: every new generation just has to learn them over again.
The first and most dangerous of these myths is the belief that putting more people on a project means it'll be completed more quickly. Brooks includes one of the most brilliant graphs I've ever seen, plotting number of women against time required to produce a baby. Would you believe it: the graph is flat at nine months, irrespective of how many women are assigned to the project. As he points out, software development is often remarkably similar.
If you're a young software developer and were at all surprised by the above, you should get hold of a copy of Brooks without delay. A few of his observations may now be a little dated, but most of it is still pretty damn relevant.