Here is an example I posted yesterday:

A boy's mother asks him where his sister is at. He knows she is in the living room watching TV, but tells his mother she is in the kitchen. The mother enters the kitchen and find her daughter is in fact there.

Did the boy lie? Yes. Why? Because given the information he had at the time, he decided to say something he knew to not be true with the intention to deceive. It doesn't matter that he was wrong and it happened to work out in the end. At the time he took the moral action, it was a lie.

A lie consists in saying something that is contrary to what you believe, not contrary to the way things really are.