Imagine you’re in an animated conversation with someone. You both laugh at something together, but then your chuckles trail off and you’re left in silence. What now?
Do you say something immediately? Do you wait for the other person to say something, no matter how long that takes? Do you jump in with whatever enters your head? Of course, it likely differs from situation to situation, but you probably average some number of seconds before you say something new if the other person doesn’t say anything, and you probably don’t stray too far from that average too often.