Why "forward" and "reverse" actually change the physics of the junction — not just which way current flows.
It's tempting to think of forward and reverse bias the way you'd think of flipping a battery on a resistor — same circuit, current just runs the other way. A PN junction doesn't work like that. The direction of the applied voltage doesn't just redirect current — it physically reshapes the depletion region at the junction, either tearing down the barrier to current or reinforcing it. That reshaping is the entire reason a diode conducts one way and (almost) not the other.