The official reason is daylight saving time (DST). The idea is to shift an hour of daylight from the morning—when most of us are asleep—to the evening, when we might actually be awake enough to enjoy it.
In the spring, we spring forward to steal an hour of morning darkness and give it to the evening. In the fall, we fall back to undo that, giving us morning light again (and sadly, making it dark by the time you finish your afternoon coffee).
The core goal? To save energy. The theory was that more daylight in the evening meant people would use fewer lights at home. Spoiler alert: modern life has kinda wrecked that plan.
