Communicating Failure

As much as I would love for things to always go perfectly, or at least to go well, I know they won't. I know that there will be times that I will forget something. Or I will screw something up. And while I can easily take responsibility, which I do. Because if I don't, then what kind of a role model am I? A bad one.
But what do I do when someone else doesn't do something. Or when someone else ignores a task? What if this person is an adult?
I struggle with this one. As a role model, it is not my place to ever place blame on anyone else. So, for at least a while, I called it miscommunication. "Oh, Lala and I miscommunicated about who was going to mail that letter" or "That didn't happen because of a miscommunication between Lala and me." And it was true, I'd contact Lala about something, and it wouldn't happen. I always figured it got lost somewhere.
But after a while, that gets old. And one of the youth called me on it. Well, R said, why don't the two of you learn to communicate?
And he had a really good point. What what happens when another adult blames another role model for 'getting in the way'? Without having the right to reprimand another adult, how do I make it clear that you just can't do that in front of these guys and gals?
Or what do I do when something gets cancelled?
Some of these challenges are things that I think about often. I never want to blame anyone else. But again, I don't want them to ever think I gave less than my all...