We talk to those who are useful to speak with

The research is appropriately hedged around with various caveats. From How stable is the core discussion network? by Mario Luis Small, Vontrese Deeds Pamphile, and Peter McMahan. From the abstract:

Researchers have paid increasing attention to the core discussion network, the set of people we turn to when discussing important matters. Because the core discussion network is theorized to be composed of people’s closest ties, not fleeting acquaintances, it is expected to be largely stable, evolving slowly over the span of people’s lives. However, recent studies have shown that networks are strongly affected by the contexts in which people interact with others, and as people experience life course transitions, they also often enter new contexts – school, college, work, marriage, and retirement. We ask whether, as actors enter new social contexts, the core discussion network remains stable or changes rapidly. Based on original, longitudinal, qualitative and quantitative data on the experience of first-year graduate students in three academic departments in a large university, we examine the stability of the core discussion network over the first 6 and 12 months in this new context. We test four competing hypotheses that focus on strength of ties, new opportunities, obligations, and routine activity and predict, respectively, stasis, expansion, shedding, and substitution. We find that the core discussion network changes remarkably quickly, with little or no lag, and that it appears to do so because both the obligations that people face and the routine activities they engage in are transformed by new institutional environments. Findings suggest that core discussion network may be less a “core” network than a highly contextual support network in which people are added and dropped as actors shift from environment to environment.

Intriguing research. Reading the details, there is a suggestion that our "core" networks are highly utilitarian - we confide and discuss with those who are best positioned to advance our agendas. Makes sense but it is not how we think of our "core" networks. This field is relatively young and I suspect part of the issue is a weak taxonomical lexicon for different types of networks.