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Simple Assumption Listing

the legs a plan is standing on

Every plan rests on things you're taking for granted. Write them down as “this works only if…”, mark which ones you actually know, and check the shakiest before you start, not halfway through.

  • KnowYou've checked it, or seen it happen.
  • ThinkIt's likely, but you haven't checked.
  • HopeYou need it to be true.
  • Easy to start
  • Medium impact
  • Learn it in 1 week
  • Ten minutes a plan
a plan, and the four legs under it
A plan drawn as a table standing on its assumptions The tabletop says “Cycle to work from Monday”. It stands on four numbered legs, one for each “only if”: the bike is road-worthy (marked know), the ride takes under 40 minutes (think), I can change at work (hope), and I'm up 20 minutes earlier (hope). The third leg is short and propped on a folded note, and it wobbles: if it goes, the plan goes. The fourth would be annoying, not fatal. At the bottom, a ten-minute check on the third leg turns its hope into know: the office has showers on floor 2. the plan Cycle to work from Monday 1 2 3 4 this works only if… 1 the bike is road-worthy 2 the ride takes under 40 min 3 I can change at work 4 I'm up 20 minutes earlier KNOW THINK HOPE HOPE [if this one goes, the plan goes] [annoying, not fatal] the ten-minute check, today Emailed the office manager. “Showers on floor 2.” HOPE KNOW

Two legs are hopes, but they aren't equal. Without a place to change, the plan is over by Wednesday. Without the early alarm, you're just late once. Check the one that would bring the table down.

Before you start the next plan

Try it now.

Pick something you mean to start this week. One sheet of paper, one sitting.

  1. Write the plan in one line

    A verb and a date: “Cycle to work from Monday”, not “get fitter”. A plan you can't picture starting has no legs to look at yet.

  2. Finish “this works only if…”

    Keep going until you run dry, usually four to six lines. Ask what you're taking for granted about other people, money, time, the weather, and your own energy at 7am.

    The ones about yourself are the easiest to miss.

  3. Stamp each line know, think or hope

    Know means you've checked it or seen it happen. Think means it's likely but unchecked. Hope means you need it to be true. Be honest: a hope dressed as a know is the whole problem.

  4. Find the leg that would sink it

    For each hope, ask: if this turned out false, would the plan fail, or just get harder? Ring the first kind. Usually there's only one or two.

  5. Check it today, in ten minutes

    Ask someone who'd know, look it up, or try a tiny version. Then change the stamp. If the answer is no, you've changed the plan for the price of an email.

Booking a weekend away? It works only if the dog-sitter is free (hope, and fatal), the train runs on Sunday (think), and you can leave work at four on Friday (hope, but you'd just catch a later train). Text the sitter before you book anything.

Try it on yours

Stamp your plan's legs.

Write the plan, then the lines that finish “this works only if…”. Stamp each one, and tick the ones the plan couldn't survive without. The sheet tells you which to check first.

    your plan

      Nothing you type is saved or sent anywhere. Copy the sheet onto paper before you leave the page.

      The planning fallacy

      Even the worst case was too kind.

      In a study published in 1994, Roger Buehler, Dale Griffin and Michael Ross asked 37 psychology students finishing their honours theses how long it would take. They gave a best guess, and a guess for if everything went as badly as it could.

      On average the theses took longer than both. Only about three in ten students finished by their own best guess. When people in the study thought aloud while estimating, they talked mostly about how the work would go, and hardly at all about how their past projects had gone: a plan whose legs they never wrote down.

      Their estimates for other people's projects were less rosy. It's your own plans you take on trust, which is why it helps to write the “only if” lines as if someone else had made the plan.

      Best guess 34 days
      If everything went badly 49 days
      What it took 56 days
      Average days to finish an honours thesis, from Buehler, Griffin & Ross, Journal of Personality and Social Psychology, 1994.

      The idea

      Why it works.

      An assumption doesn't feel like a guess. It feels like the ground. That's why it never gets checked: you only look at the things you know you're unsure of. Writing “this works only if…” turns the ground into sentences, and sentences can be wrong.

      The stamps do the second half. Most plans have only one or two lines that are both hoped and fatal, and once you can see them, checking them is usually quick. The CIA's analysts are taught the same move as a “key assumptions check”: list what must be true, and ask why each one must be.

      Keep it light

      Habits that help.

      • Start every line with “only if”. It stops the list turning into a list of worries.
      • Put yourself on the list. Your energy, your mood and your mornings are assumptions too.
      • Check hopes, not knows. Rechecking what you already know feels useful and changes nothing.
      • Stop at about six. If you're still going, the plan is really two plans.

      Go deeper

      Keep going.

      Practise this in HourLife.

      In Decisions: Assumptions. Write down a decision, weigh the options, mark the one you chose, and come back later to record how it turned out.

      Download on the App Store Download on the Mac App Store How Decisions works in HourLife