Impossible.

The document discusses pushing past limits and achieving the impossible through perseverance. It notes that things once seen as impossible, like human flight, have been made possible through determination and effort. It encourages the reader to challenge themselves by going beyond their thinking, fears, and limits in order to achieve their goals and become their best self, as the mind often imposes artificial constraints. Achieving the difficult may take time while accomplishing the impossible may take longer, but both can be done through expanding one's limits and continually learning and improving.