What does this mean? It is said, ironically I suppose, in a context of a man who spends most of his time in casinos.
a long shot:

[n] a venture that involves great risk but promises great rewards

([n] a contestant that is unlikely to win)

What's the context, Antonia?
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It was broadcasted on a short-circuit TV in a hotel, they asked Orson Welles to say sth to the guests of a hotel (In Nevada, I think)
He says: ''I've been asked by Caesar's Palace to tell you a little about gaming. I guess they've asked me because I know a little about cards, a little about history and, well, because I've been known to take a long shot or two.''
... because I've been known to take risks (more than once)
Thank you very much Pianne!!
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