We all know that if we leave behind our trash on the trails it will be left to either be picked up by some other nice hiker, or left there to decompose. Do you know how long it takes some things to decompose? (roughly...)
Banana Peel - a month Paper - a couple months Wool Scarf - a year Cigarette Butt - 10-12 years Disposable Diaper - 550 years Hard Plastic Container - 500 + years Rubber Boot Sole - 50-80 years Tin Can - 50 years Aluminum Can - 200 - 500 years Plastic 6-pack Holder - 500 years Glass Bottles - ?????
Even the tiny bits of litter that are left behind in the wilderness will, yes, eventually decompose. But they have a long term impact on the wilderness while decomposing, and that will continue even after they have decomposed.
Reduce trash before even going out. How? Well, start by repackaging all food you take with you into reusable containers, if possible. Store food in heavy duty ziploc bags that can be used multiple times!
I'm sure @treedweller has some more great tips, as this is a huge part of learning about LNT hiking!