The bill arriving afterward can return an evening from memory to calculation.

For a couple of hours the evening was simply itself: the conversation, the light, the food arriving. The bill converts it back into a transaction, and for a moment everyone is doing arithmetic about something that had stopped being about numbers. That shift is uncomfortable partly because it is so abrupt.

Settle the money as quickly and plainly as you can, either agreed beforehand or split without a long discussion. Then say something about the evening rather than the total. What you talk about last tends to be what you remember, and the arithmetic does not deserve that position.