In the 1980s, the US government launched a campaign to explain oral rehydration therapy to health workers in developing countries. Oral rehydration therapy was simple and extraordinarily effective: a child with severe diarrhoea could be saved with a mixture of water, salt, and sugar. But health workers kept getting it wrong. The problem was the explanation. It was abstract: this treatment restores the electrolyte balance in the child's body by replacing the fluid and mineral loss caused by diarrhoeal disease. Nobody remembered it. Nobody applied it correctly. Then someone found a different way to describe it: this is a magic drink you can make at home from what you already have. One litre of water, eight level teaspoons of sugar, one level teaspoon of salt. Mix it. Give it to the child. It is almost exactly what the body needs to recover. That version travelled. People remembered it, taught it to their neighbours, made it correctly. The only difference was concreteness. This is the third principle in Made to Stick. Abstract ideas are hard to remember and easy to misunderstand. Concrete ideas — built from human actions, sensory details, and specific images — stick because the brain is wired to encode them. The Heaths describe what they call the Velcro theory of memory. The brain is like a strip of velcro — information sticks when it has lots of hooks to attach to. Concrete details create those hooks. Abstractions do not. Think about the difference between these two statements about hunger in Nigeria: Abstract: many Nigerians face significant food insecurity due to structural economic challenges. Concrete: in Borno State, a seven-year-old girl named Fatima walks two kilometres each morning to a school feeding programme — because it is the only meal she will have that day. The abstract version is accurate. The concrete version is the one you will still be thinking about tomorrow. Concrete language also prevents misunderstanding. When a manager tells a team to prioritise quality, everyone nods — and everyone privately imagines something different. When she says that every product that ships must be checked by two people before it leaves the building, there is no ambiguity. Abstract communication creates the illusion of shared understanding. Concrete communication creates the real thing.