Diderot effect

The Diderot effect is a phenomenon from sociology, which was named after Denis Diderot, who first described it in an essay. In the essay, Diderot talked about a robe he used to wear in the bathroom: The old robe was a little shabby, but useful. When he was given a new robe, the new robe was more shiny, and nicer, but it did not fit well with the other clothes. 
"Regrets on Parting with My Old Dressing Gown": I was absolute master of my old dressing gown,” Diderot writes, “but I have become a slave to my new one … Beware of the contamination of sudden wealth. The poor man may take his ease without thinking of appearances, but the rich man is always under a strain.
So, the Diderot effect describes that people often show a tendency to buy more goods after they bought one item. It is said that they do this to restore the general perception they had about their belongings.