04 June 2013

Rules of Thumb

Psychologists developed a cute framework for structuring our thougths about our thoughts. Basically, you imagine two dwarves sitting inside your head, one chatty and stupid, the other lazy and slow. Here I explain how rules-of-thumb help the stupid one take over some jobs from the lazy one.

In 2004 I wrote a ‘just random’ post, which contains six guidelines for behavior. For example, the old post advises to focus each day ‘on one or at most two problems’, and motivates by saying that multitasking decreases efficiency. That old post prompted me to write the current follow-up. This post, however, contains rules-of-thumb, rather than guidelines.

What is the difference between guidelines and rules-of-thumb? I suppose the distinction is not clear cut. The Oxford Dictionaries definitions are:

a general rule, principle, or piece of advice
a broadly accurate guide or principle, based on experience or practice rather than theory

These definitions refer to each-other, and are similar, but not identical. One difference is that rules-of-thumb are based on experience, while guidelines may be based on theory. I tend to make another distinction when I use these words. Rules-of-thumb are very concrete, they have a trigger, and an imperative. In other words, they have the form if X then Y, where X and Y are both simple and objective. They resemble simple rules that we know subconsciously: ‘If I steer to the right, then the car goes to the right.’ In contrast, guidelines may involve abstract concepts, and may span paragraphs or pages: ‘You should trust medical advice more when it is based on sound statistical evidence…’ It's impossible to evaluate instantaneously whether evidence is statistically sound, and the guideline would continue with advice on how to do so. Applying guidelines requires mental effort; applying rules-of-thumb does not.

These are examples of rules-of-thumb:

  1. If you just woke up, then make sure you know the unique top priority for the day; if it's Monday, then make sure you know the top priority for the week; if it's 1st of a month, then make sure you know the top priority for the month.
  2. If an activity has top priority, then put a lower bound on the time spent on it each day; if an activity does not have top priority, then put an upper bound spent on it each day.
  3. If you want to improve something, then measure it.
  4. If you get easily annoyed, then suppress fast thinking, eat something, and sleep.
  5. If you organize things hierarchically, then aim for a branching factor ≤7.
  6. If the scope of a variable is small, then use a short name; if the scope of a variable is big, then use a long name.
  7. If reason clashes with a rule-of-thumb, then reason wins.

Having some rules-of-thumb is more important than their exact content. Let me explain. There are two ways of thinking:

  1. automatic, unconscious, and fast
    • You drive your car and you suddenly press the brake pedal. Only afterwards you realize that there's a pedestrian whose path will cross your car's.
    • Your phone is set to answer calls automatically when it is connected to a hands-free headset. Someone calls. After hearing a third of the first word, you already know it's your wife.
    • Apple, the fruit. You know it, but you have no idea how did your memory search for the definition of the word ‘apple’. You don't even realize it took any time, unless you're just learning English.
  2. voluntary, conscious, and slow
    • Compute 17×43.
    • Cancer rates increased dramatically in the past decade. This is evidence that cancer is not hereditary. True or false?
    • You and your 9 friends stand in a circle, preparing to play hide-and-seek. To decide who'll do the seeking, a designated judge goes round the circle counting to 13 (with the syllables of a song), starting from you. The 13th person, who happens to be John, is decided to be a hider, and exits the circle. Then the judge will repeat the process by starting to count from Mary, who used to be at John's right before he was eliminated. And so on until only one person is left. That person will be the seeker. Can you tell, before the judge finishes his singing, whether you'll be hiding or seeking?

Psychologists talk about System 1 and System 2. System 2 is the conscious one, and has two further properties: it has low capacity, and requires high effort. Low capacity means that it cannot do many things at once; high effort means that it gets tired and needs rest. You could imagine that System 2 is an engine that relies on a reservoir of gasoline. Two pipes are connected to the reservoir: a thin pipe that replenishes the reservoir, and a thick pipe that fuels the engine. In this analogy, the ‘low capacity’ comes from the limited debit of the thick pipe, which goes from the reservoir to the engine; the ‘high effort’ comes from the difference in pipe size, which makes it necessary to turn off the engine from time to time, while the reservoir replenishes. The gasoline metaphor may have a real counterpart: Several activities characteristic of System 2 rely on glucose.

What is the relation between System 1 and System 2? On the one hand, System 1 tends to pick up the tasks that System 2 performs repeatedly. On the other hand, System 1 incessantly emits opinions, which influence our behavior, and System 2 vets only a small fraction of those opinions. Some tasks are beyond the reach of System 1, and remain forever the responsibilities of System 2. See the examples of System 2 tasks from above. Other tasks are performed by System 2 at first and, after much practice, end up being performed by System 1. For example, the application of the rule ‘if I want to increase the speed of the car, then I press the gas pedal’ is usually automatized: Beginner drivers must consciously think about the pedal, while most experienced drivers do not.

So, where do rules-of-thumb come into the picture? All that System 2 does is tiring. But some things that System 2 does are automatizable, which means they are within the grasp of System 1. Rules-of-thumb facilitate automatization. The goal is to save energy for the important tasks, those that System 2 must vet. Thus, good rules-of-thumb talk about stuff you do not want to think about. For example, I wish that in the morning I'd just know what is my top priority, without spending time thinking about it. But I don't. The rule-of-thumb, paradoxically, makes me think more (not less) in the morning about what the top priority should be. But, the long-term hope is that in the future I'll have a habit, and I'll feel in the morning that I ‘just know’ what needs to be done.

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