Repeating relationship

I just finished reading an interview with Dan Harmon, the creator of the show Community. Both the interviewer and Dan talked about having "every relationship between every character different".

Now that's interesting.

For those of you who don't watch Community, it's a show with a large cast, and it would be so easy to have repeating relationships: multiple friendships between characters based on common interests, several mentoring relationships, or attraction between peers, etc. But it isn't that way at all. I should take more time to describe the show, but I'm going to move straight to writing.

I realized- in a blinding flash of insight- that it's easy for me to do that with the secondary characters in my MS. I might have several pairs of characters that relate the same way towards each other. Guess who's going to go back, look at all the relationships she's created, and make sure she's not being lazy with how her characters relate to each other?

One of the things that pulls me further into a story is surprise. Shouldn't the way my characters interact be surprising as well? (Not surprising as in: "Golly, Jane, I had no idea you enjoy roller derby in addition to your work CPA." Instead, the surprise should come from a weak person exhibiting strength, or from discovering a stoic character has a well developed sense of humor.

My story will be so much stronger if a character is strong with one person and vulnerable with another. That's the way we really are. I have people I'm cheerful around, and a few who will know if I've had a bad day. I might be serious with one person and never have any substantial sort of conversation with another.

Yes, the concept of non-repeating relationships is pretty basic, but it stood out to me. Had anyone else ever thought of that before?