Wild-goose chase

I went on a wild-goose chase all over the town looking for that adapter until I discovered they no longer make them.

Diagnosing this software application's problems is a wild-goose chase because it is built in an environment that has poor debugging tools.

From the beginning he has never concealed his belief that Professor Challenger is an absolute fraud, that we are all embarked upon an absurd wild-goose chase and that we are likely to reap nothing but disappointment and danger in South America, and corresponding ridicule in England.