The phrase "impossible goal" refers to a target or objective that cannot be achieved because it is extremely difficult or completely unattainable. Full definition
One of the best skills that video games can transfer into real life is the ability to attack a seemingly impossible goal until it is achieved. (thatvideogameblog.com)
The child feels he must achieve impossible goals in order to be acceptable. (religion-online.org)
Finally, thanks to my ego, I set impossible goals. (entrepreneur.com)