Idiom of the day :- A mare’s nest

Usage, examples and definition of the Idiom :-

A mare is a female horse, and we know that female horses do not built nests in trees ! That’s why a mare’s nest is either something that does not exist or a discovery that turns out to be worthless. Nelly has generously agreed to sit in a tree and provide you with examples. ‘My friend Angus says he has found a way to turn stone into gold, but I suspect it will be another one of his mare’s nests,’ Nelly said. ‘He also says he has away of knowing which horse will win in a race. I think his wisdom is something of a mare’s nest too.’