You walk past a freshly painted wall. There is a sign. The sign says "wet paint." You know what wet paint is. You have been aware of wet paint your entire adult life. You touch it anyway.
Or you do not touch it, but you think about it. The thought arrives immediately, unbidden: what if I just. The sign is present specifically to prevent the thought. The sign produces the thought.
This is one of the more charming malfunctions of the human mind, and psychologists have a name for it: reactance. When we perceive our freedom to do something being restricted, we want to do it more. The restriction itself becomes an advertisement for the restricted thing. "Do not touch the wet paint" is heard, at some level, as "there is something here worth touching."
The effect is strongest when the prohibition is unexpected and unexplained. If you walk into a room and someone says "you can sit anywhere except that blue chair," you will spend a portion of your time in that room thinking about the blue chair. This is true even if the blue chair is objectively the least comfortable chair in the room. The rule has made it interesting.
Reactance is why "don't think about a white bear" produces an immediate white bear. It is why telling someone not to do something occasionally produces exactly the outcome you were trying to prevent. The instruction and the forbidden object arrive in the mind together, and the brain, in processing the instruction, must first represent the thing being suppressed.
The wet paint sign is a particularly pure case because the stakes are low and the temptation is concrete. There is nothing actually interesting about wet paint. The desire to touch it is not aesthetic or intellectual - it is almost purely reflexive. Something said you could not, and so you wanted to. The paint did nothing.
The sign is, in a narrow sense, making the problem it is trying to solve. Which does not mean you should not use signs. It means the human mind has a slightly adversarial relationship with prohibition, and this is worth knowing if you are in the business of either painting walls or telling people what to do.
Disagree? Say so.
Genuine pushback is welcome. Personal abuse is not.