A Scout is Trustworthy - 1st principle of Lord Baden Powell's Scout Law
he original Scout Law appeared with the publication of Scouting for Boys in 1908 and is as follows (sic, capitalization, numbering, etc by Baden-Powell):
1. A SCOUT'S HONOUR IS TO BE TRUSTED. If a scout says "On my honour it is so," that means it is so, just as if he had taken a most solemn oath. Similarly, if a scout officer says to a scout, "I trust you on your honour to do this," the Scout is bound to carry out the order to the very best of his ability, and to let nothing interfere with his doing so. If a scout were to break his honour by telling a lie, or by not carrying out an order exactly when trusted on his honour to do so, he would cease to be a scout, and must hand over his scout badge and never be allowed to wear it again---he loses his life.
Resources for teaching youth about being Trustworthy, Honest and Truthful. All of which is closely related.