Context matters. I've said this for years. And now, Sam Sommers has a new book out that says the same thing. And since it is 2012, he has a brief video promotion that has inspired this post. SITUATIONS MATTER by Sam Sommers - YouTube
The idea that he talks about both makes sense and runs counter to prevailing wisdom. The prevailing wisdom is that people have a fixed way they respond to any situation - their personality. And if you understand their personality, you can then predict (or guess) how they will respond in any given circumstance.
The problem is that this isn't right. How people respond has so much to do with what is going on with them that "personality" is only one element of that. Just think about the last time you ran into screaming children (yours or on a visit to Ikea). Did you get annoyed? Did you just laugh? Something else? Is that the way you respond every time? I know that in my case, I respond differently, depending on all sorts of factors: stress, health, relationships, what you just said to me, etc, etc.
So, what do you do in response? Remember that, just like you, everyone else brings their world with them in your next encounter. What they've been reading, seeing, hearing, doing, not doing - it all creates a context for people that no one can fully know.