It's making things known, it's communicating delicate and essential information. When you're intimate with someone you are revealing your deepest nature. The real you comes through loud and clear. You are transparent, open, and vulnerable. It's a most scary time, especially if you don't know the person that well, or aren't sure that you can trust the person.
Intimacy is marked by a very close association, contact, or familiarity.
We are not intimate with people we are not close to. Associates, or casual acquaintances aren't people that we are intimate with nor are they people that we should be intimate with. A close association, a close relationship is what is required before we can hope to build our intimacy with people. Building intimacy requires association, contact and familiarity. Knowing what the person will say, how they will respond, what they smell like, what they like or dislike, how they feel about you, etc.