While his specific point is true, it is also true that delusion can be a valuable tool of progress (aka if we knew what having children is really like, the humankind may have died out). Obviously, you can't hash out a full-fledged system in a weekend, but you can get enough of a start that it pulls you in and makes you work on it after the weekend is done. Also, sometimes you can actually build a pretty sophisticated project if you have done enough of the pieces in the past. Of course, all of the above applies only to self-inflicted work; "managerial pressure" should be resisted :)