I don't think I've ever tried to chase rainbows (literally). Not even to get to the pot of gold at the end.
Chase Rainbows means to waste your time trying to get or achieve something impossible (usually in continuous tenses).
Use in Normal SpeechEdit
Ezplaining what other people may think of an ambition.
"I don't think my parents ever believed I'd make it as an actor. I think they thought I was just chasing rainbows."