The Diderot Effect is the result of the interaction between objects within "product complements", or "Diderot unities", and consumers. A Diderot unity is a group of objects that are considered to be culturally complementary in relation to one another. For example, items of clothing, furniture, vehicles, etc. McCracken describes that a consumer is less likely to veer from a preferred Diderot unity in order to strive towards unity in appearance and representation of one's social role. However, it can also mean that if an object that is somehow deviant from the preferred Diderot unity is acquired, it may have the effect of causing the consumer to start subscribing to a completely different Diderot unity.In simpler terms, the Diderot Effect describes the propensity people have to either complete a set of something or to make things match. Carried to an extreme, like some people I have known, purchase of new curtains ends up with the purchase of a new house, i.e. you need new furniture to go with the curtains, new carpeting to go with the furniture, new paint to go with the new carpets, then on to a new house for the new furniture and so forth.
This compulsion can only be overcome by recognizing the effect before the second purchase. You do not need new dinnerware because you bought a new set of glasses. Unfortunately, almost every ad you see tries to tell you otherwise. HomeDepot's success in "home improvement" depends, to a large measure, on people upgrading everything all the time. This effect is particularly pervasive in the area of fashion. You buy a new shirt and need matching tie and pants, or a new skirt and need matching blouse and purse.
Part of the effect also concerns the desire to have items that will fulfill a supposed need, i.e. if I just get a little bit faster computer, I will be able to do my work that much faster and better. Although some of these desires may be valid, to avoid a never ending spiral of purchases, you have to evaluate each purchase in terms of real value added and whether or not you will really use the newer or replacement item. If you haven't used that camera for a year, will purchasing a new one really change your pattern of use?
Being prepared includes the idea that you can actually cope with modern life and prosper, not just survive. Prosperity comes through making right choices consistently. Buying something new is not bad, by itself, but it can be, if you fail to understand that prosperity does not mean having new everything.