Strangers are strangers, thats why they create fresh aura around us and give us something which we could not expect. yes its expectation which leads relationship, personaified ideas and problems as well. Since with strangers we dont have any relationship but strange feelings, so whatever good they do gives us a new feeling, a different sense of belongingness and unfortunately it creates relationship i.e. a bond.
But there is a time gap between strange moments and relationship and this time gap is strong enough to put a deep impression provided both elements have something to express.

As a student and active listener, I am consistently engaged in dialogue with people I am not familiar with, but bound by common interest. Be it pursuit of a financial goal, or of academic interest, or perhaps simply a better fishing spot, the need to edify and add to the discussion becomes apparent when we realize how much of our experience comes from secondary sources.
Consider for example the success of the Wikipedia - a completely peer edited resource that operates without reference to author. True, it may not always be the objectively correct 100% of the time, but as concerns informal data, such as the story arc of Superman under various writers and media, there is nothing better than the cumulative input of interested but unaligned parties - that is, "Strangers" ... It's not just a social convention to see that as the case; it truly is the case.