Rules of Thumb

Rules of Thumb (Stupid Dwarf - Dopey)

How many ‘Rules of Thumb‘ do you know?

Probably more than you can remember.

How many do you live by?

Here are some popular Rules of Thumb which you may have heard of:

  • “Measure Twice, Cut Once.”
  • “Red Sky At Night: Shepherds Delight, Red Sky In The Morning: Shepherds Warning” (meaning if there is a red sky at night, the weather the next day will be dry and pleasant, but if there is a red sky in the morning the day is likely to be wet and windy).
  • “What Gets Measured Gets Improved” (This does two things: 1) focuses attention on the thing you’re measuring 2) provides a benchmark so that you can see and are more likely to aim for improvement).
  • “A Stitch in Time Saves Nine.”
  • “Tackle big or important expenses before small or everyday expenses” (if you have a big purchase to make or a bill to pay and a limited budget, taking care of the big or important thing avoids the risk of accidentally spending too much on smaller things leaving you insufficient funds to afford it).
  • “Two’s company, three’s a crowd.”
  • “If all you have is a hammer, everything looks like a nail.”
  • “If someone is remembering a situation, their eyes tend to go up and left. If they are making up a story, their eyes tend to go down and right.”

These are passed around by word of mouth, passed down from generation to generation and in some cases taught via education systems. The one thing they all have in common – they are all shortcuts. As I said at the beginning you probably have your own set of ‘rules’ that you live by without even realising. I have my own ‘rules of thumb’ for how I cook, how I drive, how I make a cup of tea, how I exercise, how I interact with others, how I write, how I choose what to watch on TV… and all of these things are shortcuts which have evolved through experience of how I prefer to do things. All of these little rules are behaviours designed to basically make our lives easier.

But why?

Humans Love Shortcuts

So that’s what we’re actually talking about here when we look at these rules of thumb.

They are just another type of shortcut.

A way of fast-tracking something, a decision or a way of breaking down a more complex piece of information in order to make a decision, arrive at an understanding or take an action.

In his book, “Thinking Fast and Slow“, Daniel Kahneman describes two thinking systems which we all have. The first is a ‘fast’ thinking system and the second a ‘slow’ thinking system.

A funnier version of this I quite like is the idea that we have two dwarves sitting inside our heads, one chatty and stupid, the other lazy and slow (but clever).

Shortcuts are what the fast thinking system uses and craves. We are programmed to make most decisions using our fast thinking systems and rarely use our slower thinking systems (because it requires much more effort).

Shortcuts are what the fast thinking system uses and craves.

In other words, shortcuts, rules of thumb, references and other biases (such as Repetition Bias or Confirmation Bias which I have written about before here: Your Own Reality (aka: How To Conquer The World)) allow the stupid, chatty Dwarf to take over jobs from the lazy, slow, clever Dwarf.

Shortcuts allow the stupid Dwarf to take over.

This also means that we are prone to be duped (in the case of marketing which plays on these biases), by media (which can subtly influence us via language and repetition) and therefore, unfortunately prone to error when these references (shortcuts, rules of thumb, cognitive biases) are ill-conceived or cynically manipulated.

So it’s OK to give the stupid Dwarf the reins, but so long as the rules of thumb are good ones (otherwise he will be far more likely to make stupid mistakes).

More Rules of Thumb: The Website

Rather than list hundreds here (and there are actually thousands – as many as you can imagine and as they are simply shortcuts for how we live our lives or make decisions you can, and do, make up your own too) I would instead like to draw your attention to a great website that I found. I have had fun looking through some of the rules of thumb on there, some of which are favourites of mine like this one about using your fingers to multiply any number by 9 (for multipliers up to 10):

Hold your hands in front of you and bend the finger down that you want to multiply by nine. Count the fingers to the left and the right of the bent finger and combine them to produce the result. Eg: for 7 x 9, bend the fifth finger down, to the left there will be 6, and to the right there will be 3 fingers standing, thus 7 x 9 is 63.

I can remember playing with this one with my kids when they were still very young – a very quick and easy way for a young child to remember their 9 times table.

The website (with thousands of Rules of Thumb organised across many categories) is

Here are some more favourites of mine from that website:

  • IDENTIFYING SEA MAMMALS: Fish have vertical tails. Mammals have horizontal tails.
  • RULE TO LIVE BY: Anything with teeth can bite.
  • MEETING DOGS & CATS: When first meeting a pet, stay still & wait for the pet to check you out first. Dogs’ order of greeting: smell, then sight, then sound. Cats’ order of greeting: sound, sight, smell.
  • BUYING AN APPLIANCE: Any gadget that does many things will do none of them as well as a single-purpose device.
  • RIGHTY TIGHTY – LEFTY LOOSEY: Homemakers and Plumbers alike use the rule of thumb, “Righty tighty – Lefty Loosey in determining the direction to turn a container cap or a pipe fitting.
  • SPOTTING A BAD CHEQUE: Ninety percent of bad cheques carry numbers below 150, indicating a new account.
  • DIETING: Most overeating happens at night. If you can’t diet all the time, diet after dark.
  • DOG DINNER ETIQUETTE: When someone else’s dog is visiting your home, always serve the host dog before the guest dog.
  • TIMING YOUR LESSONS: The most successful teaching lessons last 22 minutes, the exact length of the average TV sit-com.
  • CHECKING FOR STRESS: Warm hands indicate relaxation. Cool hands indicate tension. Place your hands on your neck, which is always warm; if they feel cool, concentrate on relaxing.
  • LIFE LESSONS: When it hurts the most, you’re learning the most.
  • THE SIX BASIC EMOTIONS: The six basic emotions are Contentment, Happiness, Frustration, Anger, Anxiety, and Depression. All other emotions are varieties of these emotions.
  • ESTIMATING WEIGHT: A “Newton” is equivalent to the weight of a small apple.
  • STRETCHING: You can’t stretch cold muscles. It’s best to do a short warm-up before stretching, or there are no gains.
  • IS IT OK TO EXERCISE WITH A COLD?: If your symptoms are above the neck (stuffy nose, sneezing), go for it. If your symptoms are below the neck (chest cough, muscle aches and pains, intestinal), skip it.
  • FINDING SMALL THINGS ON THE FLOOR: The fastest way to find a small object on its floor is to look for its shadow. Roll a flashlight around on the floor. The object may be tiny but its shadow will be big and easy to spot!
  • WHERE TO STORE SPARE PARTS: Store spare parts for an item as close as possible to the item.
  • POKER: Poker is illegal in Japan. If you’re playing poker and a Japanese person sits down, they are probably a seasoned pro who can empty your pockets in no time.
  • PACKING ANYTHING INTO ANYTHING: Always put the largest object in first and then pack everything else in descending size order. (relates quite nicely to my recent Jar of Life article btw)
  • WINNERS: Winners are simply willing to do what losers won’t.
  • SPORTS INJURIES: For pulled muscles, twisted joints, and other musculoskeletal injuries, use ice on new injuries, heat on old ones.
  • RULE OF 72: The amount of time for an investment to double is roughly equal to 72 divided by the annualized interest rate.

Final Thought

It’s not just with Rules of Thumb that we, as humans, make shortcuts.

It is a fundamental part of the human condition that we try and find quick solutions and make quick decisions. We form habits very quickly (described in detail here: Habits: How To Achieve Incredible Things) which are in themselves effectively shortcuts (because the first time we do something we take a lot longer to process everything we need to do it) – think of driving a car, the first time it is overwhelming but our brains soon find a way to shortcut the processing of all the information needed, commit the actions to ‘muscle memory’ and we soon feel like we’re driving on auto-pilot.

So Rules of Thumb help these processes and can be used to support our fast thinking systems. They can even be used to protect us from ourselves (as we are most likely to act hastily given all of the various biases we are exposed to, having a rule of thumb to refer to can be very helpful and keep us on the right track – a safety measure if you like).

Rules of Thumb are guidelines, they are not normally proven, but an indicator of some likely scenario, of our preferences or a way of condensing a large amount of information into something that’s easier to remember and therefore recall via our fast thinking system (stupid Dwarf) quickly and easily.

So look after your database of these rules, refine it (you will anyway, but now perhaps you can do so more consciously), add to it any new rules you like and delete those that don’t work for you … and just in case you get the idea you might be acting too rashly and making a bad decision, pause for a moment and let the lazy, clever Dwarf do some work for a change.

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