There are two reasons why people will lie to you, the first reason is to take advantage of you, as a form of abuse, they will either hide important information or replace real facts with fiction in order convince you to give them something, that you wouldn't give them if you would know the truth.
The second reason people lie is to protect themselves, the same way it is moral to physically hurt someone or even kill someone in order to defend yourself, it is also moral to lie in order to protect yourself. Withholding information, that if it is going to get on other people hands that are not so well intended they could use it against you to hurt you. This type of lying is called privacy, it is not information that is necessary for others to form their decisions about what they should share with you or if it is fair or not.
If you share your private information with someone who is benevolent it is not going to improve your relationship or really offer any benefit. On the other hand if this type of information ends up in someones hands that is not so well intended they could really steal from you or hurt you.
This is one of the problem we have in the modern society, with various companies collecting information's about their customers to learn how to manipulate them to spend more money in order to increase their business by offering more value to their customers. Or perhaps the worst violation of privacy is the way governments record private conversation, emails, browser history etc. of their citizens to "protect" them.
The fact that there is even a debate over the necessity for certain entity to violate privacy, it is an indication that most people lost their capacity to protect themselves, which is a common side effect of long term abuse, the victims internalize the abuse and lower their defenses because they believe that there is nothing you can do to stop it.
You are not fully protecting yourself if you are not lying to maintain your privacy, you could carry a gun lock yourself in a bunker, without privacy you are not safe.
It gets a little gray sometimes, like what do you do when someone ask your opinion about something that they are doing wrong. Like for example someone ask your opinion about what are they wearing and they are not dress well.
Telling people the truth it is hard work that it is going to require a lot of your time and energy, which you have in limited supply. If you are going to reason in a very effective way with that person, you need to take the time to ask all the questions to understand, before you state your opinions.
The same way it is not a good idea to waste physical resources, you have to be cautious with your time and energy. Intimacy is like money it needs to be earn and managed well other wise you are going to end up alone. I would take the time to be honest in a though situation with someone if he earned my intimacy, there is less of a chance for me to do it with a stranger on the street, the same way I would more likely lend money to a friend than a stranger, because there is a much less risky trade.
We all have blind spots, the nicest thing someone can do to you is to tell you the truth about what you are doing wrong, but that can go wrong, because if you are in denial you are blocking the pain associated with the negative things that you are doing. So when that pain it is brought to the surface by someone, it could be blamed on the person that brought it up rather then on the action of that individual. Because it is dangerous it needs to be earned and used with caution. Honesty is like a weapon it not only going to protect you but it is also can end a relationship or get you killed.
