The principle states that if m objects are placed in n boxes, then there is at least one box containing m/n objects or less. The implication is that the average of a set less than or equal to an element in the set.
I love a comment by George Carlin. Paraphrased, "When you think about the average IQ, remember that half the people are dumber than this!" Of course, he meant median...but with a sample size of billions, the difference between average and median is negligible.
You can use the Lambert W function to find the two solutions. The obvious one is x = 4, but there is another one which is approximately x = 0.309907. Prime Newtons has videos on how to use the Lambert W function.