Back the wrong horse
If you back or bet on the wrong horse, for example the loser in a contest, match or election, you support the wrong person. When I voted for him, I was convinced he would win, but I backed the wrong horse!
Bark up the wrong tree
A person who is barking up the wrong tree is doing the wrong thing, because their beliefs or ideas are incorrect or mistaken. The police are barking up the wrong tree if they think Johnny stole the car.
He can't drive!
Eat crow/eat humble pie
If you eat crow (or humble pie), you have to admit that you were wrong about something and apologize.
He had no option but to eat crow and admit that his analysis was wrong.
Eat one's words
If you eat your words, you have to admit that what you said before was wrong. After predicting disastrous results, he had to eat his words with the success of the new product.
This refers to a mistake made by a speaker which is considered to reveal their true thoughts or feelings.
So you got the job - I'm so sad - sorry, I mean glad!
Go up a blind alley
If you go up a blind alley, you follow a course of action which first seemed promising
but leads in the wrong direction or nowhere. The revelations promised by the suspect lead the police up a blind alley.
If you stupidly make a very serious mistake or error, you commit a Himalayan blunder.
Apparently he lost his job because of a Himalayan blunder.
Swallow one's words
If you swallow your words, you admit that you said something wrong.
He said I'd never get the job, but he had to swallow his words when I was appointed.
Wide of the mark
If something is (or falls) wide of the mark, it is incorrect or inadequate, or it is not what is required or expected. The price offered was wide of the mark - it was sold for ten times more!
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