The keeper of the vital records you need will have just been insulted by another genealogist.
Your great-grandfather's obituary states he died leaving no issue of record.
The town clerk you wrote to in desperation, and finally convinced to give you the info you need, can't write legibly and doesn't have a copying machine.
That ancient photo of four relatives, one of whom is your progenitor, carries the names of the other three.
Copies of old newspapers have holes which occur only on maiden names
No one in your family tree ever did anything noteworthy, always rented property, was never sued, and was never named in a will.
You learned that Great Aunt Matilda's executor just sold her life's collection of family genealogical materials to a flea market dealer "somewhere in New York City".
Yours is the ONLY last name not found among the three billion in the famous Mormon archives in Salt Lake City.
Ink fades and paper deteriorates at a rate inversely proportional to the value of the data recorded.
The critical link in your family tree is named "Smith".
(Source: unknown, shared with me via Email)