This is something my former colleague, Trent Brunson, told me on Twitter once that I’ll never forget. I tweeted earnestly how there were many things I wanted to share, but was concerned that everyone else knows these things already.
Trent’s (now-deleted) reply was:
I can’t think of a single time where I haven’t learned something from you. Keep sharing! Even if people already know the plot, they appreciate the way you tell the story.
So go forth, share freely, and don’t worry if the topic has already been covered, or if people are already familiar with what you’d like to share.