Take a short walk through El Parque del Buen Retiro in Madrid and eventually you are likely to encounter a peacock. If you are lucky, you will witness the full courtship ritual in action.
Iridescent tail plumage rises and spreads like a palm-leaf fan. Dozens of multi-coloured eyes reveal themselves in an extravagant display.
Make no mistake, this is quite a sight. But it frustrated the hell out of Charles Darwin.
To Darwin, you see, this spectacular sight should also have been the peacock’s undoing. Its long, trailing tail hindered its ability to travel quickly and escape predators. Peacocks simply didn’t fit the survival-of-the-fittest mould.
Instead, they relied on something else: attractiveness. A peacock’s inefficient, unwieldy tail becomes a marker of fitness when put into action in its courtship ritual.
The peacock is a good place to begin because it illustrates an important evolutionary point. As billions of human beings have moved past fulfilling basic physical needs, we have looked to add additional beauty to our own tail feathers. From the size of our house to the power of our clothing brands, when we boil down our accumulation to its root, these are our modern-day fitness markers.

The Problem with Accumulation
This shift presents two major problems:
- Excess physical possessions actually do us far less good than experiences. (In peacock-speak, as we add to our tail feathers, they get heavier, taking a toll on our physical and mental wellbeing.)
- It’s very difficult to undo. (In peacock-speak, once we think we’ve added to our tail feathers, the idea of making them less attractive seems counterintuitive.)
While our aversion to the idea of lifestyle deflation underpins the second problem, even once we’ve decided to part with some of our stuff, our innate psychology is more than capable of vetoing that decision.
Three cognitive biases in particular are leading actors in this internal anti-declutter movement. Knowing about them and honestly calling them out when we see them is critical to overcoming them.
The Endowment Effect
The first of these key cognitive biases is the endowment effect. Put simply, this is the observed tendency for us to overvalue something that we own, regardless of its real market value.
The key point here is that just our mere ownership of an item is enough for us to inflate its value. And there are few physical exceptions.
Dan Ariely outlines an experiment in his book Predictably Irrational (UK, US) whereby he raffled tickets to a major baseball game. He then asked students how much they thought the tickets were worth. Those who didn’t win reckoned they were worth $170. Those who had won wouldn’t sell for less than $2,400. Their mere ownership inflated their perceived value by more than 14 times.
Similar studies have demonstrated the endowment effect across a wide range of different physical possessions. The effect appears to be magnified by our natural aversion to losing money. That’s why, for instance, studies show that most of us would be unwilling to accept double what we just paid for a lottery ticket.
The Sunk Cost Fallacy
Second on our list is the sunk cost fallacy. This is our tendency to allow costs that are already gone (and have no bearing on future returns) to influence future decisions.
In other words, if we have purchased something, the sunk cost fallacy can make it more difficult to then make the decision to get rid of it. If you incurred $200 purchasing that coffee table five years ago, you might prefer to leave it in your garage unused than to chuck it away – simply because you incurred that $200 five years ago.
This, of course, is a thinking error. The $200 you incurred five years ago doesn’t increase the present value of the table, nor should it unduly influence a decision about what to do with it in the present.
The IKEA Effect
The undue influence of sunk costs extends beyond the financial, too. The psychological impact of a sunk cost can be compounded if we play a greater creative role in an object’s acquisition.
To illustrate this point, in 2011, Michael Norton, Daniel Mochon and Dan Ariely had participants in a series of experiments assemble IKEA boxes of furniture. Once assembled, participants were asked how much they would pay for the furniture they made and how much they would pay for pre-assembled furniture. The results showed participants would be willing to pay 63% more for the furniture they had assembled.

This effect was aptly labelled the IKEA effect, and it refers to our tendency to place higher values on products we ourselves have partially contributed to creating.
In this case, it’s our sunk labour cost – our time and effort – which distorts our valuations. And you can quickly see how this may stop us from decluttering. A self-assembled piece of furniture will be even harder to get rid of than something we simply bought.
Confronting the Psychology of Decluttering
The evidence tells us possessions that are bought and/or built are psychologically harder to get rid of because of the sunk costs we attach to them. But even if we acquire physical items through no cost or exertion of our own, we still tend to overvalue them.
To overcome these thinking errors, it’s critical to honestly reflect on if we are exhibiting them.
- Familiarise yourself with the psychology concepts. Read up on the cognitive biases. Training in these concepts has been shown to significantly improve decision making.
- Seek out and identify fair market value. Ask yourself why your valuation differs from the reality. Challenge illogical reasoning.
- Beware of mental accounting. Write off your sunk costs. They have gone and will make scarce difference to the present. Value your own contribution to a possession’s creation objectively.
The central point that underpins these actions is awareness. Understanding these concepts is key to seeing them in our own thinking. And once we see the warning flags in own thinking, we can take an objective step back and change our choices.
Why Decluttering Is a Good Place to Begin
As I have written time and time again on this blog, addressing the physical clutter that fills our homes is just one piece of the minimalist equation. But it’s an important piece.
Changing our physical environments sets a psychological precedent. It provides implicit framing for addressing other habits, such as reducing our daily decisions and number of distractions.
Our decluttering efforts are immediately visible and satisfying, and that’s what makes the psychology of decluttering is so important.
When we get over the mental blockers, our physical environments are the perfect place to begin.