1. To spare someone's feelings.
2. When to tell the truth would betray the confidence of another person who swore me to secrecy.
3. To escape an emotionally difficult situation.
4. To escape jury duty.
5. To hurt someone's feelings when they hurt my feelings first.
6. To cover up a previous lie or multiple lies, or a single convoluted tissue of lies or web of lies.
7. To make myself look smarter, more informed, kinder, more conscientious, or more honest.
8. To draw attention away from something I've done that's worse than lying, like for instance mail fraud, or perhaps kidnapping.
9. As part of a larger smear campaign against someone I find to be morally bankrupt because of their chronic lying.
10. To convince someone that I am six feet tall, have the body of an Adonis, and a penis as long and thick as my forearm (not my actual forearm, but rather the forearm of the six foot tall Adonis I lied about being).