To jettison something means to throw it overboard from a ship or aircraft, usually to make the vessel lighter in an emergency. When a hot air balloon is sinking too fast, the crew might jettison sandbags to rise back up. When a cargo ship hits a storm and starts taking on water, the captain might order the crew to jettison some cargo to keep the ship afloat.

Today we use jettison more broadly to mean abandoning or getting rid of anything that's weighing you down or no longer useful. A company might jettison an unprofitable division. A politician might jettison an unpopular policy. When you clean out your locker and jettison old papers and broken pens, you're keeping the useful stuff and tossing what you don't need.

The key idea is deliberate removal of something that once seemed valuable but has become a burden. You don't jettison things by accident. You make a conscious choice to let them go.