It is important for Scouts (and everyone else too) to be trustworthy and honourable. So, if you say you will do something, you must do it. Here is what Baden-Powell (B.P.) thought about it in his book, Scouting For Boys:
If a Scout says “On my honour it is so,” that means it is so, just as if he has 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 to be allowed to wear it again…
Often these days it is not considered that your word is trustworthy, unless you say something like “I promise”. You should always be trustworthy, by not telling lies even in games. If someone always told the truth, his friends would eventually learn always to trust him. If you only tell the truth half the time, how will people ever know when they can trust you? Here is what God thinks about it in his word, the Bible:
But let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No.’
You will make and keep a lot more friends if you do as you say you will, and do not lie.