人月神话(英).pdf

2 The Mythical Man-Month 2 The Mythical Man-Month Good cooking f akes time. If you are made to wait, it is to serve you better, and to p lease you. MEN U OF RESTA URANT ANTOINE. NE W ORLEANS 13 14 The Mythical Man-Month More software proj ects have gone awry for lack of calendar time than for all other causes combined. Why is this cause of disaster so common? First, our techniques of estimating are poorly developed. More seriously, they reflect an unvoiced assumption which is quite un- true, i.e., that all will go well. Second, our estimating techniques fallaciously confuse effort with progress, hiding the assumption that men and months are interchangeable. Third, because we are uncertain of our estimates, software managers often lack the courteous stubbornness of Antoines chef. Fourth, schedule progress is poorly monitored. Techniques proven and routine in other engineering disciplines are considered radical innovations in software engineering. Fifth, when schedule slippage is recognized, the natural (and traditional) response is to add manpower. Like dousing a fire with gasoline, this makes matters worse, much worse. More fire re- quires more gasoline, and thus begins a regenerative cycle which ends in disaster. Schedule monitoring will be the subj ect of a separate essay. Let us consider other aspects of the problem in more detail. Optimism All programmers are optimists. Perhaps this modern sorcery espe- cially attracts those who believe in happy endings and fairy god- mothers. Perhaps the hundreds of nitty frustrations drive away all but those who habitually focus on the end goal. Perhaps it is merely that computers are young, programmers are younger, and the young are always optimists. But however the selection process works, the result is indisputab