A question we’re frequently asked is whether items are allowed to move backwards on a board. Many people will just say “no” but the real answer is more nuanced than that and depends on a number of factors.
First, let me say that this question is often phrased as “Can an item move left on a board?” This assumes that boards always move left to right and while that’s extremely common, it’s not a requirement of a kanban board. It could move in any direction as defined by the policies of the board. I would suggest though that unless you have a specific reason to do it any other way, left to right is a reasonable approach that will make it easier for others to read and understand your board.
So if we assume a board where the work is flowing left to right, can we move a card backwards? This is where the actual rules of Kanban differ from the advice that I would give as a coach.
Kanban itself, doesn’t care. If your system has work going forward and then backward, the rules of Kanban are fine with cards moving in either direction.
As a coach however, I would strongly encourage you to only ever have cards moving in one direction. Why the difference?
- Moving cards backwards will complicate WIP limits. If I move a card back into a column that is now full, I’m forced to take a card that was in that column and move it even further back. Or we’re forced to violate WIP limits and neither is a good option.
- It will make a mess of your metrics. CFD diagrams and potentially even cycle times will now be skewed.
- This will hide problems in your flow. It will be harder to spot pileups in the flow if we’re moving things backwards. Work will appear to be in better shape than it really is and will make it more difficult to improve.
What does it really mean about the way we’ve modeled our workflow if we do allow our work to move backwards?
When we allow movement in both directions then we’re modeling physical states. This may be appropriate if we are in a manufacturing context where we physically move from one station to another. In the context of knowledge work, teams often interpret this as modeling the movement of work among individuals on a team. Those individuals are each seen as a separate station. If work moves from one station to another and the later station detects a quality control issue it is moved back to the previous station to fix. While this is a reasonable way to coordinate work, it does not allow for true collaboration.
When we allow movement in only one direction then we’re modelling learning states. As we move from one column to the next, we have learned new things. Moving backwards in this model would imply that we’ve forgotten anything we might have learned. In this model we are truly collaborating to move the work forward. The team is able to operate as a cohesive unit rather than as a group of individuals.
Many inexperienced teams will start by modeling physical states. We encourage them to start modeling learning states as soon as they can so that they can begin to reap the benefits of a truly collaborative team.
To summarize…
- Kanban doesn’t care if cards go forward and backward.
- We strongly recommend that you only allow cards to move forward.