How does a project get to be so late?

37 Signals tells us that Late projects are late one day at a time:

“How does a project get to be a year behind schedule? One day at a time.” -Fred Brooks, software engineer and computer scientist

There is an extensive discussion in the comments, ranging from total agreement to complete disagreement with the philosophy behind the statement. 37 Signals, for those that don't know, are a design house in Chicago who definitely do not run standard "projects." They sell flexibility and beautiful design, rather than specific features.