Clutter is the culmination of the things we collect over time. It doesn’t happen all at once. It’s the slow, quiet, duplicitous infiltration of things in our spaces. To illustrate the point, let’s go back a ways and track the typical adult's journey alongside their stuff.
Think back to your 20s. Aside from the wild parties, your life back then was probably focused on being a student, doing a little travel, preparing for a career, or generally learning how to be an independent member of society.
But after a while, you probably took your first big leap as a young adult and moved into your own place. Eventually, you got a job, maybe you upgraded your computer, replaced old posters with actual pieces of art, tastefully hung in an actual frame. Then, you moved in with someone who brought all of their stuff with them—and overnight, you doubled the volume of things under your roof.