A bet without a stake can happen when two people make a prediction or a wager purely for the satisfaction of being right. For example:
Two friends, Alex and Sam, are discussing who will win a local soccer game. Alex says Team A will win, while Sam believes Team B will come out on top. They don't wager any money, favors, or tangible stakes—they just want to see who’s right. Each is expressing confidence in something that isn't certain. The payoff is being publicly right, and the risk is being publicly wrong. My understanding is that it is these two elements (prediction and risk) that mean it is a true bet.