True but often you find, in fact all of the time I find that the ones I instantly connect with, are the ones where cultivating that connection is such a natural thing that you don't even realise you are doing it.
I don't really like spending time with anyone that I'm not connected to on another level, it's very important to me to connect to the people around me, I don't really have the time or patience for anything less satisfying than the whole package.
It doesn't have to come from a flash of vulnerability, although that does appeal to me too, it can come from shared humour too. My closest friend ever was a meeting that took less than 5 minutes of sizing each other up before bursting into laughter and realising how perfect our friendship was going to be. It was gut reactions, my intuition has never been wrong, and yet still I occasionally ignore.