Team: Nash, we estimated this user story in last backlog refinement discussion. We do not have to re-estimate it again.
Me: Have we got the information, which we were seeking?
Team: Yes
Me: Then, based on the new information, don’t you think that we have more knowledge as what needs to be done to accomplish for the story?
“Re-estimating a story is wrong. We should not waste time in re-estimation stories again and again”, I have heard this from many people. However, these people can not explain the reason why?
As per Scrum guide,
“Product Backlog refinement is the act of adding detail, estimates, and order to items in the Product Backlog. This is an ongoing process in which the Product Owner and the Development Team collaborate on the details of Product Backlog items. During Product Backlog refinement, items are reviewed and revised.”
Scrum guide suggests to review and revise the backlog items as more is known. And it definitely makes sense to re-estimate the backlog item considering the new information received. Let’s try to understand it via an example.
Around 4:45 PM, I received a call from my wife asking by when I will be coming back home. I was still at work at that time. Considering my experience of daily driving on the same route, I provided estimates of around 15 mins. So, I would be able to reach home by 5:15 PM provided I Leave at 5:00 PM.
This is an estimation based on the Priori knowledge, the knowledge that is independent of all particular experiences.
Coincidentally, I left at 5:00 PM that day, However, as soon as I pulled my car on the high way, I saw traffic, which I do not experience normally. I pulled my GPS and checked on the delay because of traffic. I called my wife and gave an estimate of 25 mins to reach home, which would make my estimated time of arrival to 5:25 PM.
This is the estimation based on posteriori knowledge, which derives from experience.
This analogy might be little off, however, sums up the concept of why backlog refinement is an important event in scrum and re-estimating a backlog item is not waste of time. On the contrary, it could help the team significantly.