Then you'll appreciate what I say about bottled porter.
It's a good thing when you have it in a tumbler, and the tumbler in your hand, and you thirsty." "It is." Callaghan spoke with conviction.

He was thirsty at the moment, and he had some hope that Meldon might possibly have the bottle of which he spoke in his pocket.

He was disappointed when Meldon went on with his speech.
"But it's not a good thing when somebody jogs your elbow and spills the whole of it over the legs of your trousers.

Now it's exactly the same with truth.

It's all right under certain circumstances.