“Mythical Man Month” is quite possibly the most oft quoted line in software. This phrase is inevitably uttered by some well-read team member when faced with a client who wants to throw more bodies at the project to make it go faster. As often as it comes up, it never really lives beyond my under-the-breath mutterings. I tend not to share it with clients. Because how do you explain the “mythical man month” to Mr. CEO In a Hurry?
Well for starters, it’s helpful to read the essay. Frederick P. Brooks warns us that in software, man hours and months are not interchangeable. You can’t add more men in order to make a project go faster. CEOs and businessey types are prone to thinking this way because it’s true in most other production settings (e.g. manufacturing or farming). It’s a dangerous myth in software for two main reasons:
[1] Programming tasks are not partitionable. “Men and months are interchangeable commodities only when a task can be partitioned among many workers with no communication among them.” Here’s a picture for graphy types:
If the tasks can’t be partitioned, they have sequential constraints. This means that increasing the team won’t bring any speed gains. It still takes 9 months to make a baby no matter how many women you add to that team.
[2] Programming requires communication. There are two types of communication: training-related and task-related.
The real drain is task-related intercommunication, which increases many-fold with each new team member. The increase in effort is in fact n(n-1)/2. So “team of 3″ requires THREE times as much intercommunication as “team of 2″. And “team of 4″ requires SIX times as much intercommunication as “team of 2″.
Any gains in task completion are saddled with huge increases in project communication overhead. And so you are no better off deadline-wise.
Wonder if I ought to carry these graphs around — ready to whip out during any client meeting. Or maybe I should memorize them and practice presenting on the whiteboard.
It’s hard to believe this was written in 1975. Things were so different then. The Mythical Man Month is a mere 16-page essay out of Brooks’ 176-page book. The other surrounding essays read like software engineering history. The Mythical Man Month reads like it could have been written yesterday.
Well, everything except for the “Man” part…
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