A lot of it has to do with time and place. If you see somebody on a constant basis and you're placed in a situation where you speak often, such as work, you might find common interests and maybe do an activity outside of work together that has to do with that. Eventually when you start doing more things together then you'll get to the point where you can feel comfortable with this person. You also have to realize that these things take time, and that closeness takes months and sometimes years to develop. Personally I have a few friends that I'm close to and that's enough for me but that doesn't mean that I don't feel comfortable or don't care about others.