chase rainbows (or a rainbow)
Pursue an illusory goal: I couldn’t afford to waste petrol chasing rainbows as far as Leeds and back...- I'd certainly understand if this purported surgery turns out to be some kind of Internet urban legend and I'm chasing rainbows, but I wanted to ask a doctor for whom I have respect.
- The latest EU attack on chemicals is just chasing rainbows.
- In these times when so many seem to spend their lives chasing rainbows, we can reflect on the great faith and fortitude of those who went before us.
See parent entry: rainbow