When the expert was thinking about the problem as a member of the project team, he was locked in the inside view—caught up in the optimism that comes with group endeavors—and did not bother thinking about what psychologists call “base rates,” that is, the average time for similar projects. When he put on his expert hat, thereby taking the outside view, he naturally thought of all the other projects he’d known and made a more accurate guess. If the outside view is fleshed out carefully and informed with appropriate baseline data, it will be far more reliable than the inside view.
