It's easy to believe, though, and most of us do it every day. For example, our commute to work is marked by the trust that other drivers will cooperate, following the rules, so that we all get to where we are going.
There are varying degrees of this through our lives, where the trust lies not in the fact that people will just follow the rules because they are rules, but because the rules set expectations, allowing everyone to (more or less) know what's going on and decide accordingly. This also makes it easier to single out the people who do not think the rules apply to them so we can avoid trusting them (and, probably, avoid them in general).
There are varying degrees of this through our lives, where the trust lies not in the fact that people will just follow the rules because they are rules, but because the rules set expectations, allowing everyone to (more or less) know what's going on and decide accordingly. This also makes it easier to single out the people who do not think the rules apply to them so we can avoid trusting them (and, probably, avoid them in general).