bet on the wrong horse
bet on the wrong horse {v. phr.}, {informal}
To base your plans on a wrong guess about the result of something; misread the future; misjudge a coming event.
To count on the small family farm as an important thing in the American future now looks like betting on the wrong horse.
He expected Bush to be elected President in 1992 but as it happened, he bet on the wrong horse.
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Source: A Dictionary of American Idioms