Final answer:
The phrase "Sky is the limit when there's footprints on the moon" is a metaphorical expression of ambition, indicating that one should not be limited by what seems impossible.
Step-by-step explanation:
The phrase "Sky is the limit when there's footprints on the moon" is a metaphorical expression of ambition. It implies that one should not be limited by what seems impossible, just like how humans were able to land on the moon despite it being considered impossible at one point. The footprints on the moon symbolize the achievements of humanity and serve as a reminder that with determination, anything is possible.