Read "Mars is my Destination" by Frank Belknap Long online for free on Textopian. Full text with search, annotations, highlights, and AI-powered reading aids.
You can be holding high cards, practically unbeatable, in the final deal of a poker game and still not be sure of winning. You have to call your opponent's hand before he gets the idea that just by drawing out a gun and shooting you dead he can gather up all the chips, and cash them in by threatening further violence. Assuming, of course, that he's capable of that kind of violence and is in all respects the opposite of an honest gambler.
You can be even less sure of winning when it isn't a game of cards you're on the point of winning, but a duel to the death with a ruthless power combine and time is running out on you.