wild-goose chase
noun
°A futile search, a fruitless errand; a useless and often lengthy pursuit.
"I went on a wild-goose chase all over the town looking for that adapter until I discovered they no longer make them."
°A task whose execution is inordinately complex relative to the value of the outcome.
"Diagnosing this software application's problems is a wild-goose chase because it is built in an environment that has poor debugging tools."