'there's got to be a pony'

In a message to my favorite Aussie restauranteur, I used the expression above. It comes from an old joke about two sons, one an optimist, and one a pessimist. I won't go into the jokes' details, but want to ask, worldwide, if that expression is used and understood?

In the U.S., yes. (Where are you?) It was one of President Ronald Reagan's favorite jokes.

Thanks. I'm in Southern California now, but have lived all over the US, and the joke seems to be well known here. I don't know about other parts of the expanse of the english speaking world.

W.Va. & Ky. -- I have heard the joke and understood it.

Ward, you're only the second person I've ever heard use it. Ronald Reagan being the first. I suspect this is a very American term, cos other than you two, I've never heard it before here in Australia.

Meanwhile, I figured out what it means by the context in which you used it, however you've got to tell me the joke sometime so I have a clue what it really means???