Why A diode is a semiconductor device with a PN junction that conducts when forward biased (anode positive relative to cathode) and blocks current when reverse biased, so current passes only one way. This is what makes diodes useful as rectifiers, converting AC into pulsating DC in power supplies, and as detectors in receivers.
Watch out A resistor limits current equally in both directions, and a fuse simply opens when current gets too high; neither cares about direction. A driven element is part of an antenna, not a circuit component that steers current.
Diode = one-way valve. The schematic arrow points the way current flows.