miss by a mile
miss by a mile {v. phr.}, {informal}
1. To shoot at something and be far from hitting it; not hit near.
Jack's first shot missed the target by a mile.
2. To be very wrong; be far from right.
Lee tried to guess on the examination, but his answers missed by a mile.
3. To fail badly; not succeed at all.
John Brown wanted to be governor but in the election he missed by a mile.
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Source: A Dictionary of American Idioms