In recent discussion (of sorts) about estimating - Not Estimating actually - I realized something that should have been obvious. I travel in a world not shared by the staunch advocates of #NoEstimates. They appear to be sole contributors. I came top this after reading Peter Kretzman's 3rd installment, where he re-quoted a statement by Ron Jeffries,
Even with clear requirements — and it seems that they never are — it is still almost impossible to know how long something will take, because we’ve never done it before.
This is a sole contributor or small team paradigm.
So let's pretend we work at Price/Waterhouse/Cooper and we’re playing our roles - Peter as CIO advisor, me as Program Performance Management adviser. We've been asked by our new customer to develop a product from scratch, estimate the cost and schedule, and provide some confidence level that the needed business capabilities will be available on or before a date and at or below a cost. Why you ask, because that's in the business plan for this new product and if they're late or overrun the planned cost that will be a balance sheet problem.
What would we do? Well, we'd start with PWC resource management database – held by HR – and ask for “past performance experience” people in the business domain and the problem domain. Our new customer did not “invent” a new business domain, so it's likely we'll find people who know what our new customer does for money. We’d look to see where in the 195,433 people in the database that work for PWC world wide there is someone, somewhere, that knows what the customer does for money and what kinds of business capabilities this new system needs to provide. If there is no one, then we'd look in our 10,000 or so partner relationships database to find someone.
If we found no one who knows the business and the needed capabilities, we’d no bid.
This notion of “I've been asked to do something that’s never been done before, so how can I possibly estimate it” really means “I'm doing something I’ve never done before.” And since “I’m a sole contributor, the population of experience in doing this new thing for the new customer is ONE – me." So since I don't know how the problem has been solved in the past, I can't possibly know how to estimate the cost, schedule, and needed capabilities. And of course I'm absolutely correct to say - new development with unknown requirements can't be estimated. Because those unknown requirements are actually Unknown to me, but may be known to another. But in the population of 195,000 other people in our firm, I'm no longer alone in my quest to come up with an estimate.
So the answer to the question, “what if we encounter new and unknown needs, how can we estimate?” is actually a core problem for the sole contributor, or small team. It'd be rare that the sole contributor or small team would have encountered the broad spectrum of domains and technologies needed to establish the necessary Reference Classes to address this open ended question. This is not the fault of the sole contributor. It is simply the situation of small numbers versus large numbers.
This is the reason the PWC’s of the world exist. They get asked to do things the sole contributors never have an opportunity to see.