Two reversals of stories you've probably heard from the pulpit at some point in time but are actually not true.

1. Myth: Sincere Means "Without Wax"

[T]he most wide-spread story is that Roman potters would fill cracks in defective pots with wax the same color as the pot and sell the pots as perfect. To convince a customer that a pot was perfect, the potter had to convince him that it was sin cera “without wax”. That has long been established as either an urban myth (or an old wives’ tale, depending on your age and slang generation). Of course, sincere does not mean “without wax” or even “perfect” so the semantic side of this proposed derivation never worked.

Sincere comes to English from Latin sincerus “sound, whole, pure, genuine” via French. Its origin is simply unknown. A possible source would be a Proto-Indo-European compound sem-kero-s “of one growth” based on sem- “same, one” + kero- “to grow”. Although semantics troubles this purely speculative derivation, too, I sincerely believe it is the most likely historical scenario for the development of sincere.

2. Myth: Jesus Talked About Hell ____ Times More Than He Talked About Heaven

Nope. Jesus talked about heaven more. Or, at least, the word "heaven" appears in more of his teaching on the kingdom and eternal life than "hell" (or Hades or whatever) does.
That one is easily verifiable just looking in a concordance or checking Bible Gateway, but the Jollyblogger did a piece on it 2 years ago.

The catch on that one is that Jesus did reference hell (or some form of conscious torment/punishment for unrepentance) quite a bit, and that alone is quite shocking to those who think of Jesus as the anti-judge.