why isn't there a commandment "Thou shall no lie" in the Decalogue?
My daughter and I disagree on this issue. I think lying is mandatory on many occasions.
For example: You just ate the most terrible apple pie in the world. The lady who made it asks, "How do you like the apple pie I made?" If God forbade lying the correct answer would be, "This is the most terrible pie in the world." If God permitted lying the correct answer would be, "It was very good, I'll have to get the recipe for that."
For example: You want a job. The interviewer says, "What is your biggest weakness?" If God forbade lying the correct answer might be very embarrassing, shameful and uncomfortable for all parties involved. If God permitted lying you would say, "If I have a weakness I am sometimes to controlling over situations because I like to make sure that it's done right or some other textbook BS."
For example: You just got fired from a job because you punched the boss in the face but nobody saw it happen. The unemployment office might require you to give a statement of what happened. If God forbade lying you would say, "I punched my boss in the face and he didn't like it too much." If God permitted lying you could say, "I'm not sure. I ask for a raise on Thursday morning and I was fired on Friday." In this case your family gets to eat food.
For example: The most famous baby killer in the world comes to your house and asks, "Where is your baby?" If God forbade lying you would say, "I hid my little baby in the closet in the far room at the end of the hall." If God permitted lying you could say, "My son took the baby to the daycare center that is conveniently located right next to the police station."
Now. What about bearing false witness. This is an evil and wicked thing. Almost everybody tells lies at some point but very few people bear false witness.
For example: I saw Steven steal $500 out of the drawer yesterday when you know for a fact that Tammy was the one who stole the money.
For example: You go to your girlfriend's house and tell your wife that you spent a few extra hours at the office to catch up on paperwork.
These are two very different things. The ethic of extreme honesty is a very self destructive pattern. I recommend that everybody should lie from time to time for protection or self preservation. Keeping your mouth shut can be very helpful too even if it causes someone to be deceived. Do not lie is way too extreme even for the Judeo-Christian God of Abraham, Isaac and Jacob. Believe me. That Jehovah guy makes some pretty unreasonable demands but I don't think He would go so far as requires to tell the truth at all cost. It's pretty ridiculous.