With a stranger, you can part when it gets slow. But with a date, you’re stuck, so you get anxious about making the experience flow. And the more you worry about making it work, the stiffer you get and the less it works. Keeping a conversation going is easier when you’re relaxed, because your brain isn’t freezing up with “Ohmigosh we’re accelerating into a dead end!” whenever it slows.
It’s also a bit about how much you care about coming across well, and how much you perceive the other person as caring about how you come across. You assume strangers and friends give you leeway for idiosyncrasies. It’s no big deal: most people have friends they would never marry. You know how it works: it’s an idiosyncrasy when you don’t have to live with it, an annoying habit when you do. And suddenly on a date, watching your partner’s reaction to something you’ve said or done, you uneasily begin to wonder if your friends aren’t more tolerant than you realize.
Then suddenly you’re terribly self conscious. You wonder which parts of your personality are the more easily digested, and if maybe you’re laying it on a bit thick too early. For example, I often deadpan lines that are intended to be humorous. It’s a technique more in use across the pond than in the USA, hence the British belief that Americans are functionally unable to recognize sarcasm. My friends are apparently broken in, but on dates I sometimes find myself lamely explaining, “Um, sorry – I didn’t mean that seriously.”
That, of course, kills things quite quickly, because another thing both partners try to do during a date is react properly to everything. Hence, laughing indulgently at perceived jokes and nodding sympathetically when you’d tell a real friend “You moron, you deserved it.” When a statement is ambiguous, it can really stall the conversation, while the other party grapples with the meaning. “That didn’t really make sense – maybe it was supposed to be funny? But it isn’t – or at least, I don’t get it. Help! What do I answer?” Instead of “Um, was that supposed to be a joke? Because I so don’t get it.”