I am not naturally what you would call a "people person," or rather, it takes so long for me to warm up to a person and feel comfortable being myself that most people don't stick around long enough.
Of course, most of anyone's day to day interactions with people are short and transactional. Picking up coffee, paying for groceries, doing that weird dance when you're about to walk into someone coming from the other direction and both of you try to move aside for the other, etc.