Definition
Curiosity, in Rosling's sense, is the disposition to notice when reality contradicts your expectations and to treat that contradiction as a clue worth following.
It is not idle interest. It is the active attention that says "that's odd — why?" instead of "that can't be right." Rosling treats curiosity as the foundational virtue of factfulness because every correction in the book begins the same way: somebody noticed a number that didn't match their picture and chose to investigate rather than dismiss.
Why it matters
How it works
The disposition has a recognisable rhythm. A piece of information arrives that does not fit the existing picture. The curious response is to lean toward it: read more, ask another question, look up the underlying data. The incurious response is to discard it as anomalous, noisy, or politically inconvenient.
Rosling's career is essentially a long catalogue of such moments. A student claim, a survey result, a chart that did not match the textbook — each one was treated as a thread to pull rather than a nuisance to bat away. The pulls accumulated into a corrected map of the world.
Curiosity pairs naturally with intellectual humility. Humility makes the contradiction possible — you have to admit your current picture might be wrong before "this is odd" can register at all. Curiosity then supplies the energy to do the work of revision. Without the second, humility decays into shrugging; without the first, curiosity has nothing to feed on.