When I started writing I Wish... I had a very long, and possibly heated, conversation with my sister about lies. We found that most reality-based fantasy books relied heavily on lying in order to move the plot along without stopping to explain everything to each person they pass in the book. Now, as a parent, I hate lying. Really, truly do... but as a writer, I can see its merits.
I included a clip from I Am Number 4 because it is one of my favorite YA movies, and yet the entire plot is based on secrets and lies. The main character has to lie to his friends, the girl he loves, law enforcement, and occasionally his father-like guardian, and everything is wrapped up tightly with secrets. It's truly appalling how often this happens throughout the movie, and yet... I still love it.