Sooner or later, we get caught lying. For most of us, it's incredibly early in life, and the falsehood detected is innocuous. We're scolded, briefly punished, and then allowed to go about our day. This happens with some regularity until our authorities trust in our awareness of morality.
It's not always entirely clear whether or not a child has truly learned any distinction between right and wrong or whether they've just begun to understand the tolerance of certain authorities for lying. Maybe grandma and grandpa will let me get away with something mom and dad won't. Very early, we learn to play to the crowd, to feel out an audience's tolerance for bullshit and to stay just shy of that.