I came across this quote while reading Ira Flatow's wonderful book - "They all laughed"
The Law of Firsts (as in who discovered it first) was hypothesised by Eliot Sivowitch of the National Museum of American History.
“Whenever you prove who was first, the harder you look you will find someone else who was more first. And if you persist in your efforts you find that the person whom you thought was first was third.”
Of course, applying the law means that at least two other people said it before Eliot.