Refer to the passage: The history of mathematics is filled with episodes in which concepts initially rejected as nonsensical were later found to be indispensable. Negative numbers were once described as fictitious and were treated with suspicion even by competent mathematicians well into the eighteenth century. Imaginary numbers, despite their unhappy name, turn out to be central not only to electrical engineering but to the formulation of quantum mechanics, where complex amplitudes encode the very behavior of subatomic particles. Non-Euclidean geometries were initially regarded as curiosities until Einstein showed that the actual fabric of spacetime is non-Euclidean. This pattern — of conceptual scandal followed by triumphant application — suggests something about the relationship between mathematics and the world. Either reality has remarkable affinities with the abstract structures the human mind invents, or our minds, having evolved in this universe, are predisposed to invent precisely the structures that describe it. The choice between these explanations matters less, perhaps, than the recognition that what we now treat as obvious was once, for someone, an outrage. The final sentence ('what we now treat as obvious was once, for someone, an outrage') primarily means: