Developers are not hot-swappable

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Thursday, January 24, 2008

DeliveryFocus.net – Developers are not hot-swappable

I wish more people would realize that just because people have similar skill-sets doesn’t mean they’re interchangeable.  It seems to be a common problem amongst senior management where I work.

Posted in Computers | 1 Comment »

One Comment

  1. Stephen says:
    2008/01/28 at 4:02 pm

    This is part of the title story of Fred’s Mythical Man Month. It’s more than just “if it takes a woman 9 months to have a baby, then 9 women can have one in one month”.

    A task is estimated to take 10 man months, but they want it in 6 months. So they put 2 people on it. At the end of month 2, they realize that they aren’t 33% through the task, they’re only 20% done. So the new estimate is (1 / 20%) * 2 people * 2 months = 20 man months. They’ve put in 4 man months, so there are 16 more months. They still want it at the 6 month mark, which is 4 more months. So 4 mans should do it. They hire 2 more mans. At month 3, they discover that nothing has been accomplished (because not only were the new people coming up to speed, the 2 original people were doing the teaching). So they do the above math again and hire even more.

    Brooks’ law is that adding people to a project makes it later. Brooks has acknowledged that there are exceptions. That doesn’t mean that your project is exempt, of course. The exceptions are, well, exceptional.

    When you add to this logic the fact that managers underestimate tasks, and even fixed price bidders do too, you get really good reasons why 60% to 90% of new projects are delivered late or not at all. It might be noted that managers generally underestimate even when senior staff suggests more reasonable estimates. In the past 25 years, i’ve had perhaps one manager use my estimates without pressuring me to reduce my estimates. That’s alot of managers. Nearly a statistical sample set.