What does “Explain it to me like I’m a 4 years old” mean?

The quote got famous by the courtroom drama Philadelphia, where a lawyer was fired by his law firm when they discovered that he was HIV positive. Today it is an oft-heard cri de coeur from entrepreneurs, managers, policymakers and other professionals who are tired of the empty phrases of management bullshit and want to grasp a subject in a clear, understandable way.

How do you explain complex concepts such as net present value, subsidiarity principle or unconditional love in an understandable way? It seems that it takes more insight from a person to explain something simple than something complex. Perhaps that is why Einstein is reported to have said: “If you can’t explain it to a six-year-old, you don’t understand it well enough”.

In their book, professors Steven Sloman and Philip Fernbach give the example of toilets. Everyone knows the phenomenon of a toilet: a ceramic bowl filled with water. You press a button or a lever and the water, and everything in it, is sucked into a pipe and discharged into a sewer. But how exactly does this work? A group of Yale students were asked to rate their knowledge of some everyday objects (such as a toilet, a zipper or a cylinder lock) on a scale of ten. They were then asked to describe in detail how these objects function. This seemed much more difficult than expected.