Generally I'd diagnose something as a black hole if the scope is larger than 2 days' worth of work, but I may call something a black hole even if it's estimate is only one hour. The key here is that I don't see a way to deliver the card in the estimated amount of time. If the cause is simply a bad estimate and it takes maybe 50% longer to complete, that's not a black hole. But if the problem is that we didn't realize the extent of ripple effects, the incomplete dependencies, or the sheer overwhelming volume of work ahead, then it's a black hole.
When we see a black hole, we have a few options:
- break up the pair to see if we can get another expert opinion on how to clear the technology hurdle
- break up the pair to see if we can find a way around the hurdle (why climb a mountain if there's a tunnel through it?)
- involve the customer to see if we can trim the scope
I'm not sure who came up with this name, but I'd like to thank Chris Joiner for it because he was always the best at recognizing them, and in Toyota Production System terminology, he was most willing to stop the production line to get rid of black hole cards.