I have friends who have always been very conscious of the monetary cost of items, but seemed to think space is free (that is, "hoarders"). They very recently began a transition away from that, triggered partly by the local health department and partly by a worsening medical condition leading to full-time wheelchair use. It's fascinating to see people who spent decades accumulating stuff suddenly getting rid of it and turning down new free stuff, all because their valuation of "space" changed.

One of the reasons simplicity is hard is that owning stuff has psychological connotations for everyone involved. A digitial copy of your photograph or document "in the cloud" seems less permanent and less under your control than one on your hard drive, which itself seems less so than a physical copy -- and this perception is at least partly mistaken. Those seeking control and "certainty" may still accumulate paper copies far beyond what is reasonable, all because they have a psychological desire to do so.

IMO, it all boils down to how we value space, time, money, effort/frustration, certainty/risk, efficiency, and a whole host of other factors -- and how accurately we understand those factors. Remembering to account for "a few feet of counterspace" or "a week getting stuff done" are key to simple living.