Onions in the Varnish:
In The Periodic Table, Primo Levi tells a story that happened when he was working in a varnish factory. He was a chemist, and he was fascinated by the fact that the varnish recipe included a raw onion. What could it be for? No one knew; it was just part of the recipe. So he investigated, and eventually discovered that they had started throwing the onion in years ago to test the temperature of the varnish: if it was hot enough, the onion would fry.
Chesterton's Fence:
In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, 'I don't see the use of this; let us clear it away.' To which the more intelligent type of reformer will do well to answer: 'If you don't see the use of it, I certainly won't let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it.'
Chesterton's Lamp-post:
Suppose that a great commotion arises in the street about something, let us say a lamp-post, which many influential persons desire to pull down. A grey-clad monk, who is the spirit of the Middle Ages, is approached upon the matter, and begins to say, in the arid manner of the Schoolmen, “Let us first of all consider, my brethren, the value of Light. If Light be in itself good—” At this point he is somewhat excusably knocked down. All the people make a rush for the lamp-post, the lamp-post is down in ten minutes, and they go about congratulating each other on their un-mediaeval practicality. But as things go on they do not work out so easily. Some people have pulled the lamp-post down because they wanted the electric light; some because they wanted old iron; some because they wanted darkness, because their deeds were evil. Some thought it not enough of a lamp-post, some too much; some acted because they wanted to smash municipal machinery; some because they wanted to smash something. And there is war in the night, no man knowing whom he strikes. So, gradually and inevitably, to-day, to-morrow, or the next day, there comes back the conviction that the monk was right after all, and that all depends on what is the philosophy of Light. Only what we might have discussed under the gas-lamp, we now must discuss in the dark.
Bike-shedding (Law of triviality):
"The act of wasting time on trivial details while important matters are inadequately attended is sometimes known as bikeshedding. That term originates from Parkinson's observation of a committee organized to approve plans for a nuclear power plant. As Parkinson noted, the committee devoted a disproportionate amount of time to relatively unimportant details -- such as the materials for a bicycle storage shed -- which limited the time available to focus on the design of the nuclear plant."
Yak-Shaving:
Yak shaving is what you are doing when you're doing some stupid, fiddly little task that bears no obvious relationship to what you're supposed to be working on, but yet a chain of twelve causal relations links what you're doing to the original meta-task.
Bullet-Tracing (Survivorship Bias):
WW2 engineers in the U.S. are looking at planes and deciding where to increase armor plating. They take "heat maps" of where planes returning from combat missions have been hit with enemy fire and draw what seems to be a reasonable conclusion: "Let's put the plates on the places where these planes are getting shot." Abraham Wald wisely points out that they should do the inverse of this because the marks on the planes returning show "what kind of hits planes can take and survive to return".
Well-Pissing:
A man lives in a house with no bathroom and every night at midnight he has to pee. He walks 200 paces from his house and relieves himself. One night, he is very tired and decides he doesn't want to walk 200 paces. He stops at his well (which is only 10 paces) and makes a deal with himself: "I'll pee in the well, just for tonight, but I'll take care to sample the water tomorrow morning. If it tastes bad, I'll go back to walking 200 paces." He samples the water the next day. To his delight, he doesn't notice a change in the taste. So the man decides he will start peeing in his well every night.
Goodhart's Law:
"When a measure becomes a target, it ceases to be a good measure".
It is named after British economist Charles Goodhart, who advanced the idea in a 1975 article on monetary policy in the United Kingdom:
Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.
Gold-Plating:
Working beyond the scope of the mission when no one requested it (in a group setting or project).
Frog-Swallowing:
"When one's job is to swallow a frog, it's best to do it first thing in the morning."
Or colloquially: "Do the hardest thing first".