I'm not sure that there is a universal social contract in place. There are many situations where a lie is acceptable or even expected.
In business dealings it's acceptable to lie about the price you are willing to pay (or receive) for a service. It is however completely unacceptable to lie about business finances when communicating with investors or the tax office.
Even in personal matters, if someone told you information to keep in confidence, and then someone else asked if you know anything about it, it is acceptable (even honorable) to lie to maintain the trust with the first person. However, there are also situations where revealing the information to the second person is the more honorable action.
In business dealings it's acceptable to lie about the price you are willing to pay (or receive) for a service. It is however completely unacceptable to lie about business finances when communicating with investors or the tax office.
Even in personal matters, if someone told you information to keep in confidence, and then someone else asked if you know anything about it, it is acceptable (even honorable) to lie to maintain the trust with the first person. However, there are also situations where revealing the information to the second person is the more honorable action.