Rhys knew exactly why there were nights when I would cling tighter to him, why there were moments in the bright, clear sunshine that I would grip his hands. He knew, because I knew why his eyes sometimes turned distance, why he occasionally just blinked at all of us as if not quite believing it and rubbed his chest as if to ease an ache.”
-- Feyre (1 )

Importance: Feyre is talking about the insecurities that arise when memories of the past prompt them to think about the terrors of the recent battle. Rhysand and Feyre are mates, which is a formal bond between faeries. They have a deep connection that provides them with a deeper-than-normal level of understanding.

We keep away to let you have your privacy, but don't think for one moment that there isn't a single one of us who doesn't know and remember, who isn't grateful that you came here...
-- Ressina (4 )