talking

why is it that with some people you never know what to talk about, but then with others conversation just flows?
Even with people you might have something in common, sometimes you just end up talking about the weather, just to avoid staring at each other. Sometimes you find an excuse to leave, because staying means awkward silences... while with other people time just flies by. With some people you just talk, you just know what to say... you might not even know that person that well, but for some reason something makes you react...
I wish I always had something interesting to say...