Echoes and shifts.

I read Speaker for the Dead years ago and passionately hated it, but it has one scene that's always stayed with me. The most interesting character in the novel is Jane, an artificial sentience that makes herself known to the protagonist Ender and piggybacks on his experiences via an earpiece he wears. At some point in the story (my memory is fuzzy), Jane distracts him while he's talking with another character and he temporarily turns off the earpiece. The next few pages describe the minute, complex, instantaneous effects of this action on Jane, who must completely restructure herself to adapt to this sudden disconnection from him. This is the only thing I remember from that entire book, and after I talked with Evan this afternoon, clicked End and put the phone back in my pocket, I realized that this transformation had suddenly happened to me. Our week apart and that conversation have shown me that Evan is living his own life now, and the connection between us has been severed and replaced with something else. The old me that was attached to him can no longer exist.

The only difference is that I don't have the efficient immediacy with which Jane recreated herself-- only that sudden awareness of isolation, need, and infinite loose ends.