Marek Kohn was discussing trust on Thinking Allowed. You can see it all the time in the hospital, that patients/families seem to think that you might actually not have their best interests at heart, and would do something/not do something harmful, just because…  Well, I don't know why, out of pure badness?

He pointed out that trust essentially is the expectation that others will take your interests into account, so it depends on "having confidence in your ability to predict how others will behave. This confidence will be supported by shared culture and norms: if you know that others have grown up with similar ideas about how to behave, you can answer the question of how they are likely to act by asking yourself: "What would I do if I were in their position?"" Reminds me of Richard Holloway's comment that hatred is failure of the imagination; to trust also requires the ability to imagine another person's thinking, including being able to understand why they might not always be able to act in your interests. 

So in mixed societies eg San Fransisco, people are less likely to trust their neighbours than in places like Dakota. 

Of course, faith depends on the inability to prove something, so people with religious faith tend to find it easier to trust.  Or should that be the other way round?

He argues that language would never have developed without trust.  Because talking about something, when "words are cheap", is much less reliable than action.

It is a form of social capital, so if you want to be able to benefit from it, then you must also invest in it, by being trustworthy yourself.  And that also depends on an equitable relationship.  Overlaps a bit with respect too.