A backlog is a stock and only the outflow shrinks it
💎CORE ARGUMENT
A backlog is not a list of things to do. It is a quantity, like water in a bath, and it obeys the rule every quantity of that kind obeys: its level changes only through what flows in and what flows out. Reordering is not a flow. A prioritisation session moves items up and down inside the bath and leaves the water exactly where it was.
This explains a feeling I had for years and could not name. The Monday after a careful grooming session, the backlog is better sorted and precisely as heavy. We worked on it for two hours and did nothing to it.
Only two taps matter. One is the inflow, which I rarely control, because customers and colleagues are entitled to ask. The other is the outflow, and it has two outlets: finishing an item, or deleting it. Deleting is the one people forget, and it is the cheap one. An item nobody has touched in a year is not waiting. It has already been decided against, and only the record disagrees.
My proof arrived in the summer. When the Exceptions and Tracking teams merged we inherited two backlogs, and the instinct in the room was to interleave them into one well-ordered list. We deleted first and ranked what survived, and the merged list came out lighter than any amount of ranking could have made it.
The same arithmetic runs my reading pile, the itch list and a dispatcher's screen at nine in the morning. If the level bothers me, the question is never what comes first. It is what leaves, and how fast.
Where I might be wrong. Some stocks should be high. A long list of ideas costs nothing as long as nobody mistakes it for a promise; my claim is about backlogs people feel as debt.
And the bath has a flaw as a picture: water is all alike, and backlog items are not. One item can be worth the rest together, which is the case a pure flow view cannot see.
🧱BUILT FROM
🌍WHY IT MATTERS
- In planning I ask for two numbers before any ranking: what came in last month and what went out.
- Every grooming session ends with deletions, or it was a reading group.
- I stopped calling a sorted backlog under control.
☑️NEXT STEPS
- Add inflow and outflow counts to the monthly planning page
- Delete everything untouched for twelve months before the merge
- Try the same count on the reading pile
A stock changes only through its flows. Everything here is that sentence applied to a product team.
💎 A bottleneck sets the pace for everything upstream of it says where the outflow is throttled. 💎 Working memory holds a handful of things so the list must hold the rest says why a list this long stops being a list at all.
A stock has a level. Flows change the level; sorting does not. A backlog's only outflows are completion and deletion, so any activity that is neither leaves the load where it found it, however much effort it took.
Order is not nothing. When items differ a hundredfold in value, draining quickly in the wrong order is its own waste, and a good ranking is what makes a small outflow count.
It became the issue that travelled, a way to put numbers on the queue with 📐 Little's law, and the first rule of the merged roadmap: delete before ranking.