Every post I see on Facebook is unhappy at the Trump victory. All of them. Yet I know that about half the people in the US don't feel that way.
This means that I'm seeing a *very* biased sample. This means that I'm mostly out of touch with how Americans feel. That's probably not too important, since I don't live in America, but it's made me think. There's probably other matters where I'm in an echo chamber of people who think like I do. Brexit, for example.
But it isn't just politics. There's other subjects where I'm in an echo chamber - computer security, for example. Everyone I see posting on Facebook thinks that computers are very insecure, and that this is important. Yet I think that most people don't agree, or at least don't care.
Which echo chambers are you in?