Le Chatelier's principle states that when a system at equilibrium experiences a stress, it shifts to counteract that stress. Increasing pressure favors the side with fewer gas molecules. Here, the reactant side has 3 moles of gas (2SO₂ + O₂), while the product side has 2 moles of gas (2SO₃). Thus, increasing pressure shifts equilibrium toward products, increasing SO₃ yield. This occurs because the system reduces pressure by decreasing total gas moles.