Yes, a bullet can physically hit and even penetrate a plane, but the consequences are often less dramatic than what is depicted in movies. Modern commercial aircraft are built with a thin aluminum or composite skin; if a small-caliber bullet punctures this skin at high altitude, it creates a small leak. Because the cabin is pressurized, the outflow valve system will simply adjust to compensate for the minor loss of air, and the plane can continue flying safely. However, a "critical hit" is a different story. If a bullet hits a window, it can cause a rapid (not necessarily explosive) depressurization. If it hits critical wiring, the fuel tanks, or the hydraulic lines, it could lead to system failures or fire. While planes are remarkably resilient and a single bullet hole is rarely a "catastrophe," any projectile hitting a high-speed, pressurized vessel is considered an extremely serious safety event that would trigger an immediate emergency landing.