The thing where you assume that, if any important information exists, that it would have reached you through your existing channels.
It’s like an assumption of an “ideal” information environment? Or in the high value of your own network, and in the lack of value in other networks?
(like an academic who assumes no novel idea for his field can come from an anonymous internet blog)
It’s a kind of cognitive bias - it should be calibrated. You can test the rate of useful ideas that do not originate in your network.