Example is the school of mankind, and they will learn at no other.

People copy what they see far more reliably than they follow what they are told. Instruction has to compete with everything else in the room, while example does not, because it is simply the observable fact of how things are done here. This matters most for anyone with children, juniors, or anybody who watches them. What you actually do is the whole curriculum.

Pick the lesson you have been repeating without effect and ask whether you model it. Change your own behaviour for a fortnight and stop saying it altogether. Most of the teaching you do happens when you are not trying to teach.