Screw-You effect: a type of demand characteristic, where participants work out the purpose of the experiment, so behave in a way opposite to what the experimenter want to find.
Texas Sharpshooter Fallacy: where people overestimate the similarities of, and links between, small pieces of data with no real connection, and use this to claim a pattern exists.
Ikea Effect: the tendency for people to like something better, and gloss over its flaws, if they had a hand in its creation.
Above-average/Below-average Effect: the tendency for people to believe they will be better than the “average person” at easy tasks such as simple sums or driving, but worse than the average person at stereotypically difficult tasks like chess or juggling. (Also known as the Lake Wobegone effect, which would have qualified for that list itself.)
Marshmallow Effect: a way of testing kids’ ability to delay gratification and decision-making. In the study, they were left alone in a room with a marshmallow on a plate, and if they could resist the temptation to eat it for 10 minutes, they would be rewarded with two marshmallows. This might not sound like the most exciting study in the world, but when the original study was followed-up, the kid who could delay the urge to eat their marshmallow were found to be more successful as adults. So, evidence that marshmallows are good for you?
Hedgehog’s Dilemma: A term created by Schopenhauer to describe people in social or intimate situations. A hedgehog, because of its spikes, cannot easily get close to other hedgehogs, so it’s desire for companionship cannot be achieved without causing pain. In the same way, people desire to be close, but in order to be close they have to risk causing, and being caused, pain by doing so.