Messy Bedrooms

Why is it that no matter how you train your kids to pick up after themselves they still end up with messy bedrooms? I'm sure some of it is due to us not standing there and watching them clean up their rooms, and some of it is just in the nature of playing with things. The crazy thing is it's not a toy issue. It's books, and shoes, and lip gloss and earrings! The hardest part is I remember clearly keeping my room a mess when I was a kid, and since Zach's room is my old room it's sometimes hard to get after him about it. So, I guess I just have to live with it, or work with both kids to pick up the mess. Getting rid of half of their things would help too. Something I'm secretly working on each day while they are at school! I suppose that sounds heartless but truthfully they would never know if things went missing, as I'm only getting rid of clothes and toys that they never wear or play with. Hope I get done before June 11th!