Recently, I've been seeing a new phrase around. boing boing currently has it on its masthead as the 'phrase to live by'. It's everywhere, and it is, "Don't tell me the sky is the limit when there are footprints on the moon".
It almost makes you cry with the soaring fabulousness and human yearning inherent in the precise and crispy wording, doesn't it? However, "the sky is the limit" already means that there is no limit. "Don't tell me the sky is the limit" makes no sense. If you think the existing catchphrase was intended to crush people's native imagination and will to succeed, then you are poor at English.
It's still a nice phrase though.