A quote from Happy Catholic’s Quote Journal:

Martin: Does that make you truly happy?

Douglas: Oh, well come on. No one’s truly happy.

Arthur: I’m truly happy.

Douglas: No, Arthur, you are cheery. No one’s interested in the secret of true cheeriness.

Arthur: That’s not true. I’m fairly often just completely happy. Like, for instance, when you get into a bath quickly and it’s just the right temperature and you go, “Ohhhhh…” I mean no one really gets any happier than that.

Martin: What a depressing thought.

Arthur: No, no, it’s not though! Because those sort of things happen all the time, whereas you’re hardly ever blissfully happy with the love of your life in the moonlight. And when you are, you’re too busy worrying about it being over soon. Whereas the bath moments, there’s loads of those.
Cabin Pressure, “Fitton”