Why do we hold on to clutter?
According to the study below “examining an item for longer periods of time resulted in greater attachment to the item and thus higher valuations.” Since we spend a lot of time with our clutter we become attached to it and place high valuations on it (endowment effect).
Simply touching an item increases the odds of purchasing it. This explains why retailers go out of their way to ensure we touch products (try the clothes on here, touch the fabric, find your size, test drive the car, etc.)
The duration of ownership has been shown to increase the valuation of items that people currently own as well as items they have owned in the past, a phenomenon termed the “length-of-ownership effect.” We hypothesize that the duration of exposure to an item will foster increased pre-ownership attachment to an item and increased valuations in a manner similar to duration of actual ownership. We examine this effect in two experiments, both variations of the classic mug experiment. To induce different levels of exposure, we varied the amount of time that participants examined the auctioned item (i.e., coffee mugs) prior to participating in real dollar auctions. In the first study, participants bid in online English open bid auctions. In the second study, participants bid in first-price sealed bid auctions. In both cases of duration of physical contact positively influenced valuations (i.e., bid levels).
Paco Underhill's bestselling book Why We Buy: The Science of Shopping.
Source: The power of touch: An examination of the effect of duration of physical contact on the valuation of objects (pdf) and Lifehacker article.