The phrase denotes an bold, seemingly not possible endeavor. It characterizes actions which might be audacious, bordering on the fantastical, and sometimes exceeding typical limitations. As an idiom, it paints an image of somebody trying to attain one thing perceived as completely unattainable.
The implied significance of endeavor such an bold job resides within the potential for transformative impression, even when the literal purpose stays out of attain. The trouble and innovation required to even try the not possible can result in surprising breakthroughs and developments. Traditionally, many scientific and technological leaps began as ideas deemed unrealistic, highlighting the worth of pursuing daring visions.