Usually either not finishing or not having the energy to keep up with the maintenance and the actual every day enjoyment of an organized system.

If you've got a messy underwear drawer, that's OK. Good organization doesn't mean that all your panties are folded, ironed and in color order. Believe me mine aren't, and I still consider myself organized.
Ask yourself does this system work? If you can reach in and find what you are looking for and get dressed in the morning, then you are good. Don't fix something that isn't broken. A messy underwear drawer that functions effectively means you are still organized.
It seems easy enough I know, but I think too many people try to do too much, and end up doing nothing because it seems too hard.
If you feel unorganized start with the thing that annoys you the MOST.
Ask questions like:
Why doesn't this sytstem/area work?
Why is it so messy/cluttered?
Why cant I ever find what I'm looking for?
When coming up with a system to make an area work better I think about the simplest version of that process. The easier it is, the easier it is for everyone to get on board (including yourself)
My second tip to being organized is don't stress the small stuff. Work on the area or areas that need the most help. Once you've figured out the problem area, think about the easiest solution.
Good Luck!
If you have something you'd specifically like me to write about, click on the contact button and email me with the subject Organization Series. I'd love to hear from you.