Use a weighted decision matrix when options exceed 3 and criteria exceed 4 — working memory cannot hold all dimensions at once

Why This Is a Rule

Miller's law limits working memory to approximately 7±2 items. A decision with 3 options and 4 criteria requires comparing 12 cells simultaneously — already exceeding working memory capacity. With 5 options and 6 criteria, you're comparing 30 cells. Intuitive comparison at this complexity doesn't produce "gut wisdom" — it produces systematic errors: overweighting the last criterion considered (recency), overweighting the most vivid criterion (salience), and ignoring criteria that are hard to evaluate (avoidance).

A weighted decision matrix externalizes all dimensions onto a single surface where they can be compared systematically. Each option is scored on each criterion, scores are multiplied by criterion weights, and totals reveal which option best satisfies the weighted combination of all criteria. The matrix doesn't make the decision — it makes the comparison tractable for a human brain that can't hold 30 comparisons in working memory.

The 3×4 threshold is specific: below this complexity (2 options, 3 criteria), intuitive comparison works well because the comparison space fits in working memory. Above it, externalization becomes necessary. This gives you a clear trigger for when to invest the 15-30 minutes a matrix requires versus when to decide intuitively.

When This Fires

• When facing a decision with 3+ options and 4+ evaluation criteria
• When intuitive comparison feels circular — "I keep going back and forth" is the symptom of exceeding working memory
• For one-way door decisions (Classify every decision as one-way or two-way door before deliberating — minutes for reversible, days for irreversible) that warrant structured deliberation
• When multiple stakeholders need to see and agree on the evaluation logic

Common Failure Mode

Using matrices for simple decisions: building a weighted matrix to choose between two lunch options wastes time and creates false precision. The matrix is a power tool for complex multi-dimensional comparisons. For 2-option or 2-criteria decisions, a simple pro/con list or direct comparison suffices. Match the tool to the complexity.

The Protocol

(1) When a decision involves 3+ options and 4+ criteria, externalize into a matrix. (2) List criteria in rows, options in columns. (3) Assign weights to criteria before scoring any options (Assign criterion weights before scoring options — knowing scores first lets you unconsciously rig the weights) — this prevents weight manipulation. (4) Score one criterion at a time across all options (Score by criterion across options, not by option across criteria — column-first prevents halo effects from inflating favorites) — this prevents halo effects. (5) Multiply scores by weights and sum columns. The highest total is the analytically preferred option. (6) Check: does the result match your gut? If yes → decide. If no → the gap between analytics and intuition contains important information. Investigate what your gut knows that the matrix doesn't capture before overriding either.