For What It’s Worth: Rule of Thumb
By Joel Dresang
A rule of thumb is a generalized guesstimate, an educated approximation, a guideline based on reiterated experience. It’s inexact advice you should take with a grain of salt because results may vary.
A rule of thumb is a handy standard that broadly can apply to a situation without bothering with the details.
The origin of the term logically comes from using one’s thumb as a portable ruler. Just as a cubit is the approximate length of a forearm, an inch is about the width of a thumb. Of course, thumbs come in all sizes, so a rule of thumb is a ballpark estimate.
The thumb figures its way into many common expressions, including those of measurement. Thumbs up is a sign of approval, while thumbs down is rejection. Thumbing your nose (while wagging your fingers) is a more aggressive gesture of disapproval, an insult that dates back at least to the 17th century. Even earlier came the custom of biting one’s thumb at a rival, as portrayed in Shakespeare’s “Romeo and Juliet.”
For What It’s Worth is an occasional look at the meanings and origins of words and expressions investors may encounter.
The thumb plays a pivotal role in manual dexterity. Having a green thumb makes you a natural gardener. To have someone under your thumb means you have control over them.
In some European traditions, you hold your thumb to wish good luck, much as crossing your fingers ties your hands, letting you concentrate on whatever you’re pulling for. On the other hand, a true display of idleness is twiddling your thumbs.
Yet, there’s strength in diversity. As useful as thumbs are, we need other fingers. So, being all thumbs is considered clumsy and ham-handed, which could make you unwillingly conspicuous–sticking out like a sore thumb.
Joel Dresang is vice president-communications at Landaas & Company.
(initially posted April 28, 2017; updated February 17, 2020)
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