Distinguish diagnostic trees (why?) from solution trees (how?)

Use a "why?" tree to find root causes and a "how?" tree to generate solutions — mixing them produces confusing structures.

Why it works

Diagnostic trees ask "why is this happening?" — each branch is a potential cause or contributing factor. Solution trees ask "how could we achieve this?" — each branch is a potential approach or lever. Mixing the two structures confuses causes with solutions, which in turn produces interventions that treat the wrong thing. Distinguishing them keeps the analysis phase and the solution phase separate, preventing premature closure on a solution before the diagnosis is complete.

How to do it

1. At the top of the tree, label it clearly: "Why?" (diagnostic) or "How?" (solution/option generation).
2. In a diagnostic tree, every branch should be a statement of fact or a hypothesis about causes.
3. In a solution tree, every branch should be an action, a lever, or an approach.
4. Do not start the solution tree until the diagnostic tree has identified the root cause you are targeting.

Evidence

Separating diagnosis from solution generation is a principle in management consulting, design thinking, and clinical medicine (differential diagnosis before treatment). The cost of premature closure — solving the wrong problem — is documented in both organizational and clinical decision-making literature. (mechanistic)

The separation is a discipline, not always a sequence — sometimes generating solutions reveals overlooked diagnostic dimensions (solution-informed diagnosis). Strict separation can sometimes be counterproductively slow.

Common mistake

Building a solution tree and calling it a diagnostic tree — branches like "improve training" and "increase headcount" are solutions, not causes, and their presence in a diagnostic tree means the analysis jumped to answers before finding the problem.