The problem is that this is demonstrably untrue; for example, "A perfect and just weight shalt thou have; a perfect and just measure shalt thou have; that thy days may be long upon the land which the LORD thy God giveth thee." (Deut. 25:15)
So where did we get this idea that there are only two? Is it a garbled version of the story of Elisha ben Avuyah witnessing a lad who fatally fell off a ladder while shooing away a mother hen to fetch eggs for his father?
I have been unable to find any citation for this incorrect assertion, yet when I talk to people about it, everyone seems to have heard it. So I'm casting my net to, well, the Net: Have any of you ever seen this assertion in print? Preferably with a source?