Think about a wardrobe - it is a specific fixed size, with it's physical structure setting the boundaries. If it was designed to comfortably accommodate 20 hanging garments, but you have stuffed 50 in there, then you are not respecting the boundaries of the wardrobe, and in fact you are not respecting the garments either, because they have no room to "breathe" and are getting all wrinkled and are not being worn because you can't even see what you've got in there any more, and when you can't be bothered trying to force another item in there it gets chucked on the closest piece of furniture or horizontal surface. (Same goes for the overstuffed shed, kitchen drawers, toy box..... etc).
Your day is the same - the fixed length of 24 hours sets the boundaries, but because they are not tangible or visible, it's even more difficult to respect them.
Then there are all sorts of things that have no boundaries at all, and if you do not establish some for yourself you are going to be in big organising trouble! There is no limit to the flow of information, entertainment, work, requests, demands, email, junk mail, and so on. If you were not able to set (and stick to) boundaries with all this coming your way, you would end up being consumed by the internet and cease to be a functioning member of society! Obviously this is an extreme case, but I'm sure you get my point. Not operating within appropriate boundaries which you set for yourself and your lifestyle can lead to a frustrating overflow of stuff cluttering up your mind, your time, and your to-do list.
To use boundaries effectively, start big and break the area down into smaller and smaller areas, until you have well-defined homes for everything. If you have a place for everything, it's much easier to have everything in its place. Your actual home is the first boundary, which is broken down into smaller functional zones (the different rooms) which contain appropriate things, and then those rooms are further broken down into smaller areas (wardrobes, kitchen cabinets etc). Within those you can use drawer dividers, shelf dividers, storage boxes, or other tools to establish further boundaries or specific homes for items (for example a box for batteries in the kitchen "junk drawer").
The concept of boundaries does seem restrictive at first, but really they provide a framework within which to operate, so you know exactly what goes where, and what you have in each specific zone. And respecting those boundaries means items are better looked after and much easier to keep to organised.
So what boundaries can you set in your home and life to get more organised? I would love to hear from you!