Why would the amount you worry about disease be a significant predictor of the a mount you worry about social relationships? After all, you might have had a history of dependable and reliable relationships, but some unsettling brushes with disease. The answer must be that the menta mechanisms that underlie worrying about disease share brain circuitry with the mental mechanisms that underlie worrying about other things. Any variation in the responsiveness of those shared circuits will show up in all kinds of worrying, not just one kind. It’s a bit like a car. The handbrake and the footbrake do different jobs and have some separate components, but they also rely on the same hydraulic system. As a consequence, a loss of brake-fluid pressure will show up in reduced effectiveness in both brakes. The more two components draw on shared machinery, the greater the extent to which the performance of one will be a predictor of the performance of the other.

Daniel Nettle, Personality: What Makes You the Way You Are, Oxford, 2007, pp. 50-51