Why is the Literature Review--often the most difficult chapter to write? What do you think are some of the most common mistakes people make when conducting a review of the literature and/or writing t

Why is the Literature Review--often the most difficult chapter to write?  What do you think are some of the most common mistakes people make when conducting a review of the literature and/or writing the literature review chapter?

Please no more than  225 words and internet reference for verification.