a mare's nest
A difficult, complicated, or confusing situation. The tax laws in this country are a mare's nest that nobody fully understands.
a mare's nesta wonderful discovery which proves or will prove to be illusory.
A mare's nest is here being used to symbolize something that does not exist, as horses do not make nests. The phrase is first recorded in the late 16th century, as is the variant a horse's nest , although the latter is now no longer in use.
a ˈmare’s nest
1 an idea or a discovery that seems interesting and exciting but is found to be false or have no value: I fancy this will prove to be a mare’s nest! We have had these mysteries before.
A mare is a female horse or donkey. They do not make nests and so a mare’s nest does not exist.
2 a difficult or complicated situation; a mess: This area of the law is a veritable mare’s nest. ♢ My hair is a mare’s nest!