Interestingly, I've found these percentages seem to hold true in a variety of other social situations as well. Online dating, for instance - I find I get responses to about 30% of initial messages, but 2/3 of those are just being polite and never strike up a conversation, so I end up with RL dates with about 10% of initial prospects. Haven't met one yet that I felt a real connection to, but I've only been on 8 dates so far, so 1% would imply I've got a few to go.

Or college. I figure I knew (had some interaction with, could name & recognize by sight) perhaps 300 people at my college. Maybe 30 of them I'd call "friends" - I could sit down with them at the dining hall without feeling awkward and chit-chat about classes or hobbies or interests or society and politics. Only about 2 or 3 of them did I really feel close enough to to stay in touch with them after college, once our common interests had ended.