The enemy had two machine gun emplacements creating a crossfire; one was to the south, and the other to the north. The one that Gao Yang had to take out was the machine gun position to his south.
Gao Yang didn't even know the exact location of the machine gun emplacement, not just its orientation, but he also didn't know the relative position of the machine gun muzzle and the outer side of its fortification. It's somewhat complicated to explain; in simple terms, the machine gun was hidden deep inside a hole, and to get the bullets into the firing port of the machine gun, he had to find the right angle.
The shot Gao Yang had to make was extremely difficult; he needed to first find an angle to fire at the machine gun and take out the one on the south. However, by doing so, he would expose himself to the northern machine gun. The enemy's two machine gun positions created overlapping fields of fire and could cover each other.
