Waiting for confirmation
It was in the mid-1970s (yes, before the Internet and nonstop news cycles), and on the West Coast, LAPD had arrested a suspect in the notorious Hillside Strangler murders. By middle of the overnight, around 2am eastern, Associated Press wires had moved a story and a mug shot with the name of the suspect, for the AM-Cycle papers to use. For some reason, probably because I had to be awake to do hourly newscasts during the overnight, I fixated on the fact that this poor bastard was being named as the Hillside Strangler before even being charged with the crimes. I thought, "what if he's not guilty?"
So I didn't use his name on my overnight newscasts. I also alerted the overnight news editor at the co-owned newspaper so that we at least waited to see...and by 6am, the police had released the suspect and said he was no longer a suspect. But thanks to the AP, I believe most newspapers in the AM editions carried his photo and his name, and probably ruined the rest of his life (not much to ruin, he was a career criminal anyway, as I recall, but he wasn't the Hillside Strangler).
The best rule of thumb is the one Dan Rather attributes to Walter Cronkite's UPI training in The Camera Never Blinks: "Get the story. Get it right. Get it out first."
Too many people not picking up on the second sentence in that advice.