Novel information and job leads travel through weak acquaintances, because strong ties already share what you know.
Granovetter's 1973 paper, from a study of how people found jobs: most heard through acquaintances rather than close friends, because close friends already know what you know.
In practice
- A job that was never advertised is filled by someone the hiring manager met once at a conference.
- A researcher's most useful reference comes from someone in an adjacent field they meet twice a year.