Robert Browning is quoted as having remarked, "Ah, but a man's reach should exceed his grasp, or what's a Heaven for?"

This line, as well as the one above, point to ambition as requiring goals that may extend beyone one's reach. While these goals may be beyond reach, yet, in the striving a person's exceeds his/her realistic expectations.  For instance, if students set their goals for grades at Bs, they may achieve those Bs, or they may just miss them and make C+s.  However, if these same students set their sights at As, some will actually make the A, and some will not get an A, but they will earn a solid B instead of the C+, the "mud." 

When one has goals that are set high, the result may not be reached, but success is still assured.