There is someone I know who is an amazingly good at his job. He probably puts in more hours than anyone else I know and he does it because he sincerely loves what he does. And it is infectious; everyone around gets caught up in the passion for the work and strive to do better. It’s a virtuous cycle of benefit to the entire group and he does it out of honest joy. Now imagine if he were to point the fact that he works so many hours. What do you think everyone would assume about his motivation to work so hard? Sure some may miss that detail or even chalk it up to him being informative but for some, it will plant that seed of doubt. That question of, “Does he do this just so he can hold himself up for doing it?”
When you live out a behavior, you inspire those around you. But when you speak of it, even if only to inform and truly not to brag, you lessen the effect of that example.