We spend huge amounts of our lives surrounded by "stuff." Piles of possessions. Mountains of things: things we bought, things we were given, things we don't even remember how we came to be in possession of.
And we spend so much time with these things of ours, that at some point we stop seeing them. We stop seeing the piles of clutter as piles of clutter - they just become part of a daily landscape.
We know the piles are there, and that they are clutter, and that we should probably do something about them, but that never quite happens.
And at some point, the clutter becomes comfortable - familiar. We get attached to our piles of possessions, so that when we do decide to tackle our piles - thoroughly and completely, once and for all - it's a very intense experience.
It turns out that many of us, don't have lots of experience detaching ourselves from our possessions - that's why it's so important to have support when you do a major clean out. Where that support specifically comes from doesn't matter quite as much as making sure you have it.
Support can come from friends or family members, an online community, a book, or even a professional organizer - we just need someone to help us get all the way to the end.
Cleaning up, clearing out, and taking an honest look at everything we own is an extremely intense process - it's why we work so hard to avoid it.