21 times.

In his book Making Vision Stick, Andy Stanley says that is how often a vision needs to be communicated in order for it to stick.

To paraphrase him: About the time you, in a leadership role, are tired of repeating the same vision over and over again, those listening for the vision are just beginning to hear it.

In other words, just when you think that everybody should have gotten it by now, they are just beginning to get it.