This one turned out to be wrong
One investigation, from the first guess to the verdict that killed it, with the evidence still attached.
Pose a hypothesis
Write down what you think is true before you go looking. One card, at the start, so it can be wrong in public later.
Gather evidence
A stack of interview notes, a churn number, a pile of support tickets - whatever you actually have. Group it into sections and link it to the claim it speaks to. The evidence that contradicts you stays on the canvas too, so nobody can quietly drop it.
Reach a verdict
The verdict sits on the canvas with the evidence still wired to it. Somebody asks later and the reasoning is right there underneath the answer. An insight worth keeping gets promoted out to the workspace, so the next investigation starts with it instead of from zero.
None of this is a new idea
Writing down what you expected and what you found is old advice. The missing part was a question that visibly closes. The guess at the top of this page is still up there, wrong in public, with the evidence attached.