Why do we buy things we don't necessarily need? The origins of that question actually lie in history, and more specifically the history of capitalism. "Disposable income" has only really been a thing for a couple of centuries, at least for everyday people (of course, kings, queens and nobles have always been able to flash the cash). As various mechanisms in the history of capitalism made people richer — from the shift to agriculture to the Industrial Revolution — the number of people with money to spend on non-essentials expanded. The creation of a middle class was a particularly vital element in the development of shopping for "fun."

Throughout history, the middle class has tended to be aspirational: it has wanted to look good and separate itself from the lower rungs. The key to that is often the purchase of stuff, particularly stuff that sends a specific class signal (which changes from society to society). But the purchase of non-essentials is generally a signal of wealth— a sign that you have enough money to buy a brass coat peg in the shape of an owl, or an ornamental typewriter, or thousands of books, and therefore don't have to confine your spending purely to food and board. This is partially why the concept of changing fashions developed. As clothing technologies shifted and became cheaper, people of different classes also became more able to own clothing for different occasions, and to buy new clothes as the old ones went "out of fashion."

When it comes to the here and now — a world where possession accumulation is viewed as a natural part of life, and ascetics who go without extra clothes, sofas and ornamental candleholders are viewed with suspicion (or are selling you something) — the origins of our object-attachment often start quite early. In fact, when we're very small, many of us develop an incredibly strong attachment to one particular object.

For some of us, it's a bear or a stuffed toy, for Linus from Peanuts, it was, famously, a blanket. We find this object incredibly hard to release and many of us hold onto it into adulthood. Christian Jarrett, writing for the British Psychological Society on "stuff" and how we relate to it, explains that this is often viewed as a "transitional object" because it helps us become slowly independent of our mothers. He details experiments in which children refused point-blank to take a perfect copy of the loved thing instead of the thing itself. One of our first relationships is often with this object.

We possess a wide variety of attitudes towards our stuff: Some people will just enjoy accumulating goods, while others will worship the objects they have. A study from 2011 gave us a particular insight into what happens with the second sort of love for possessions, particularly in men. This worshipful love of possessions is the kind of thing that makes people wash their cars obsessively, make sure that their antique rifle is in absolutely perfect condition, and insist on everybody in the house admiring their chosen delight at least once. (Accumulating love can be part of the same impulse: people who collect objects, like stamps or dolls, are creating a collection to worship as a whole.)

The 2011 study found that men who are particularly lonely are more prone to feeling intense worshipful connections which resemble passionate love towards their various possessions. Cars, computers, bicycles and guns were the specific items up for examination in the study, but others are likely part of the same impulse. Feelings of love, essentially, have to go somewhere, and so, in some cases, we may lavish it on an inanimate thing.

An expert told New Scientist that the things we buy and accumulate are often "repositories of ourselves" — basically, we curate our stuff as an exhibition of our own lives, as much as we possibly can. This is particularly the case in life periods where self is in flux or open to new influences: teens have been shown to be particularly prone to putting their self-expression into possessions, from beaten-up sneakers to posters, fashion and music.

People who have just gotten married often have a similar kind of experience, as they frequently feel that objects they've been gifted as part of their registry project a certain idea of married self-life that will shape their future.

Possessions can make us feel better and more secure in ourselves; they can reiterate identity in a worrying situation; or they can reinforce certain self-images ("we are the sorts of people who have a dumb pillow shaped like a pineapple, because we are whimsical and travel a lot"). Ironically, it's possessions that often provoke the most envy in others and create distance and dislike for those who are truly affluent, according to studies. The phenomenon of frustration when one's possessions don't match up to one's self-image, aka "champagne tastes on a beer budget", is traced to this idea. Our possessions are supposed to mirror us, to others and to ourselves.

The big reason we hold onto things is that they're not just things to us. A cheese knife is not really just a cheese knife; our feelings about it include how we came to own it, how we used it, and the memories we attach to its use. We have practical possessions (and impractical possessions that we believe will one day become practical), but much of our "stuff" is in our lives because of this type of attachment.

A famous 1995 study identified four major different categories of attachment we feel towards the non-utilitarian stuff in our lives: stuff that reminds us of other people, stuff that expresses individual identity, stuff that isn't absolutely necessary and could be disposed of, and stuff that inspires ambivalent feelings (a mixture of pleasure and irritation, for instance). Things can be in more that one category at the same time: a soup ladle can be both utilitarian and a gift from a much-loved parent, for instance. Items that fit into the two first categories are the ones most likely to be accumulated over time because of our attitudes about the importance of memory and self.

Throwing those things away is also perceived, consciously or not, as a kind of threat. "Possessions with such properties become an extension of the self... therefore, the loss of these possessions is a threat to self-identity," researchers argued in the Journal Of Consumer Psychology in 2010. "The loss of special possessions elicits strong negative reactions because special possessions are identity markers, and the loss of an identity marker is a symbolic form of death of self." Things root us in one place and root our selves more firmly in the world.

This, in a nutshell, is why you keep all the random stuff you inherited from your grandmother and why you keep buying specific items for yourself over and over until you form a collection (antique poison rings, perhaps, or a screen-printed cushion cover of a pug). They're reinforcements of particularly important types of identity, and we keep them as armor just in case that identity is under threat. That explanation may not bring much comfort to the roommate who's been complaining about how much of the living room has been consumed by your novelty teddy bear collection, of course. But it's worth a shot.