I was reading today an article on 5 things to know about being friends with an INFJ. This hit the nail on the head, and really liked it. Want to get to know an INFJ? Spend time one-on-one. I'll let this fifth point make the case I'm trying to say. A lot of non-INFJs do not realize this, though it's hard to know this when they don't know much about MBTI types.
For me, a friendship does not always become solid until this happens...
5. If you want to get to know us, hang out with us one-on-one.
It’s only in private that we show our true colors. Think of us as roly poly bugs. If we are overwhelmed or startled, we curl into a protective, hard ball. We’ll sit and watch conversations but rarely contribute with personal substance. But if we are comfortable, we will be more open. Some of the best conversations I’ve had occur when I’m spending one-on-one time with someone. For example, one of my best guy friends and I had a very personal, hour-long conversation about snow and what it symbolized to each of us. It reminded him of his travels and the friends he met in places that snowed. For me, snow is the promise of Christmas and sweaters and all things comfortable. So, if you truly want to get to know us, get us alone. We might talk your ear off.