1. “Readers feel smart because often they’re figuring out the clues before the book’s characters do” (You feel smart.)

2. “There’s a sense of mystery, challenge and then clean satisfaction in figuring out a code, whether you’re 10 or 80″ (Puzzles are fun.)

3. “[Jesus] not only had sex but also spawned a secret family line continuing in the present day” (Sex.)

4. “Brown taps into the uncertainty most of us feel in fancy museums” (You realize that even the experts have a lot to learn.)

5. “Enticing characters are the sine qua non of popular novels” (Engaging characters.)

6. “Clever escapes, midnight flights, desperate chases down dark corridors proliferate” (Solid plot; many twists and turns.)

7. “The reading public has always loved stories that chip away at establishments” (Pick a big, big, big topic.)

Do you have any other ideas about the success of The Da Vinci Code? How about the bandwagon effect or herding instinct? Similarly, what about word of mouth? And, how big was the marketing budget for the book?

Why The Da Vinci Code has sold 43 million copies…