mare's nest

a mare's nest (a hoax or an illusory discovery; || а confused mess; a place, condition, or situation of great disorder or confusion ) иллюзия, заблуждение; нечто несуществующее || полная неразбериха

Example 1: You have such a tiresome habit of being right. But if it's all a mare's nest we shan't be pleased with you, you know. (A. Christie, ‘The Labours of Hercules’, ‘The Lernean Hydra’) — У вас такая невыносимая привычка всегда быть правым, но если на этот раз вы попали пальцем в небо, то нам, знаете ли, это не доставит удовольствия. (Кунин)

Example 2: The previous two sheets of this piece are a mare's nest of scratched out half sentences, words replaced and replaced again and clauses arrowed in or arrowed out. (Gary Covington, Learning to Write, 2007)

find a mare's nest (to make what you suppose to be a great discovery, but which turns out to be all moonshine) ≈ попасть пальцем в небо; попасть впросак

Example: The sole evidence against this view of the case was police evidence; and the police were naturally reluctant to admit that they had found a mare's nest. (B. Shaw, ‘Cashel Byron's Profession’) — Единственное, что шло вразрез с этой точкой зрения, — улики, собранные полицией. А полиция, конечно, не хотела признать, что попала впросак. (Кунин)

Frequency of usage: rarely