Why do large projects go over budget?

“There are three kinds of lies,” the old saying goes. “Lies, damned lies, and cost projections for big projects.”

Yes, yes, the third item in the old saw is supposed to be statistics. But you, too, might feel the substitution appropriate if you’d just read How Big Things Get Done, an indispensable if perhaps unduly optimistic response to the tendency of modern projects, like California’s US$9 billion high-speed train project, to go, um, off the rails...