By saying or seeing or being one thing, and then its opposite, Mercury's dualistic approach lets him perceive the polarities, discern the differences, and then conceive the central sameness. He'll argue both sides of an issue to convince himself he has seen the whole truth and settled on what he sees as the central truth. He'll study seven separate philosophies to see the similarities and conclude a common thread can lead to a central truth. Though often accused of obfuscation, fickleness, flightiness, fence-sitting or phoneyness, mercurial minds are merely on a mission to seek understanding, or teach truths, by seeing or showing the point between two opposites. Comfort is between cold and hot.
X marks the spot where two separate lines connect.
But he has to try the two, or imagine both boundaries, before he finds his middle ground. Up and down are two sides of the same coin. Day and night are two sides of the same Earth. Intellect and imagination are two sides of the same mind. Good and evil are two sides of the same person.