The keeper of the vital records you need has just been insulted by another genealogist.
Your great-grandfather's newspaper obituary states that he died, leaving no issue of record.
The will you need is in the safe on board the Titanic.
Copies of old newspapers have holes occurring only on last names.
John, son of Thomas, the immigrant whom your relatives claim as the family progenitor, died on board ship at age 10.
The public ceremony in which your distinguished ancestor participated and at which the platform collapsed under him turned out to be a hanging.
When at last after much hard work you have solved the mystery you have been working on for two years, your aunt says, "I could have told you that!"
The relative who had all the family photographs gave them all to her daughter who has no interest in genealogy and no inclination to share.
The only record you find for your great grandfather is that his property was sold at a sheriff's sale for insolvency.
The one document that would supply the missing link in your dead-end line has been lost due to fire, flood or war.
The town clerk to whom you wrote for information sends you a long hand-written letter which is totally illegible.
The spelling of your European ancestor's name bears no relationship to its current spelling or pronunciation.
None of the pictures in your recently deceased grandmother's photo album have names written on them.
No one in your family tree ever did anything noteworthy, owned property, was sued, or was named in wills.
You learn that your great-aunt's executor just sold her life's collection of family genealogical materials to a flea market dealer "somewhere in New York City".
Ink fades and paper deteriorates at a rate inversely proportional to the value of the data recorded.
The 37 volume, sixteen thousand page history of your county of origin isn't indexed.
You finally find your great grandparent's wedding records and discover that the bride's father was named John Smith.
Your grandmother's maiden name that you have searched for for five years was on a letter in a box in the attic all the time.
You never asked your father about his family when he was alive because you weren't interested in genealogy then.