Also, this is great for relationship advice too. Personally, I always struggle with asking too many yes/no or how many questions rather than asking why/how questions. Givers vs Takers aside, if I had to guess, I'd say that "doorknobs" can be created by saying or asking something the gets you to explore each others' opinions and experiences.
I also thought the part about how sharing boring mutual memories is more fun than exciting individual memories is interesting, but maybe not a hard rule to follow. I've been more interested in scuba diving recently because of some of the awesome stories my friends have told me.