A few reasons why an author might choose to use a pseudonym:

1. He's unsure whether the book will be successful, and doesn't want to risk ruining his name and reputation.
2. The book divulges personal and sensitive information, and he doesn't want to walk down the street to meet the stares: "Oh, there goes the pathetic loser who was/did..."
3. The work challenges some very powerful interests and the author would rather that they not know who he is...

Let me introduce you to a different anonymous writer: Moses.

He's the one who transcribed the Torah, hence the name "Five Books of Moses." Torah was his passion and love, his life and legacy. He spent 40 days and nights in heaven, learning Torah from G‑d Himself.

He wanted to be part of it with all his heart.

But he was willing to give it all up for something dearer to him than the Torah -- the Jewish people. The same people who, since the beginning of his leadership, spat him in the face time after time: "Why did you take us out of Egypt?" "Do you want us to die in the desert?" "We are starving!"

Yet, when this ungrateful stiff-necked people sinned with the golden calf, and G‑d decided to wipe them out, Moses begged G‑d to forgive His people. "And if You decide not to forgive them, please erase me from the book that You wrote!"

Moses was willing to say goodbye to his magnum opus, to erase his name from the history books, because he was a leader. A true leader.

In the end G‑d forgave the Jewish people. But in order to teach future generations the meaning of true leadership, Moses' name is not found in an entire section of the Torah, the reading of Tetzaveh.

Ironically, it was his quest for anonymity that gave him his unparalleled place of honor in the annals of history.