Break Big Questions into Smaller Ones

"Will our home renovation be finished before Chinese New Year?" Answer that directly and you'll probably just say "70%, I guess" based on gut feel.

Ask it differently: what all has to go right for it to be done in time?

• Will the tiles and cabinets arrive on schedule?
• Can the carpenters and painters fit you into their schedules?
• Will the plumbing and electrical inspection pass the first time, with no rework?

Each smaller question is far easier to answer than the original: you can ask the suppliers, ask the foreman, or check what happened to neighbors in your building.

How to break it down

• When everything must hold, multiply. Say delivery is 90%, scheduling 85%, and inspection 80%, and they're roughly independent. The chance all three go smoothly is 0.9 × 0.85 × 0.8 ≈ 61%, lower than the gut-feel 70%. This is the conjunction effect from lesson 1.3.
• When any one path will do, add. For "I'll get to see an old friend this weekend," it could happen because he passes through my city on a business trip, or because I travel to his. If the two can't both happen, add their probabilities: say, 30% + 25% = 55%.
• Watch for correlation. If the sub-questions are linked (a reliable foreman tends to make both delivery and scheduling go smoothly), simply multiplying will underestimate the total, so adjust upward a bit.

Find the key uncertainty

Once you've broken it down, look for the sub-question that is both the most uncertain and the most decisive. That's your key uncertainty: the thing most worth researching now and keeping an eye on later. In the example above, if the inspection is the biggest unknown, start by asking about this contractor's rework rate.

Why decomposing helps

• It turns a vague hunch into a set of numbers you can check.
• It tells you what information to go and collect.
• When the outcome is in, your review can pinpoint which link went wrong.