I’m currently reading Agile Estimating and Planning by Mike Cohn, one of the things he discusses in the early chapters is why so many of projects fall behind. Many of his ideas fall in line with Eli Goldratt’s thinking in The Goal and what is described as The First Way in The Phoenix Project.

Mike discusses Parkinson’s Law which postulates that work will always take the time allocated to it. In other words if you’ve got a project and a deadline you won’t finish early because you’ll use the remaining time to refine, improve, and polish the work.

He also discusses an idea raised in The Goal where tasks are dependent on each other. In Eli Goldratt’s book Alex realises the importance of interdependencies when he takes the boy scouts walking through the woods. Cohn uses the example of developers and testers and how the person doing the QA cannot begin until the functionality has been created.

If you combine these two theories you realise that if tasks only run late, never early and the subsequent tasks can never begin until the previous one has finished you end up with an ever slipping schedule. If each task misses it’s deadline 10% of the time then once you’ve multiplied up by the number of tasks the probability that your delivery will run late climbs very quickly towards a statistical certainty!

So what can we do about this? Build in contingency? This is a risky strategy as if the team (or even you) know that there’s flexibility built into the schedule then the work will continue to consume all available time.

One approach I’ve heard a lot more recently is to allow projects to be constrained by either time or feature lists but never both. In a time based approach functionality is ranked in order of importance and when the clock runs out the project is delivered (regardless of whether or not all features are complete). In a feature driven release (for example in a lean MVP project) then the team will continue to work until all features have been completed – regardless of how long that takes.

Personally I’m much more of a fan of the first approach. By keeping this prioritised list transparent with the clients and stakeholders you can work on exactly the right work. Your work is cut when the time runs out (rather than adding low value features and running over) and one of my favourite reasons for adopting it – if a project does take less time than you expect your client gets more functionality for their money instead of feeling ripped off by inflated estimates, that’s something I’d certainly appreciate as a customer!

What do you think? How do you agree on project deadlines and commitments?