Importantly, you don't get to learn from your mistakes in "opsec." Dread Pirate Roberts asked a question about connecting to a tor site using curl on StackOverflow under his own name. Seconds later he realized "D'oh, that is in hindsight a bad move." and changed his name to a pseudonym.
Choose your own adventure:
a) He got to learn from his mistake.
b) That incident was recounted years later in the criminal indictment.
That was pretty shocking to read in the indictment.
He obviously didn't think it was a serious issue at the time, but jesus, could you imagine how it felt to read about that one mistake years later? Makes you wonder what you have left online that might bit you in the ass years from now. I know i certainly couldn't run for office now!
It's not clear that was a mistake. The indictment merely lays out relevant evidence in chronological order, not in investigative order: we don't actually know how the FBI cracked DPR and found Ross Ulbricht. My own favored theory is that they only learned DPR==Ross Ulbricht in early 2013 when DPR paid for the first hit (of Curtis Green) by wiring 2 bank payments from an Australian bank account (Ulbricht lived in Australia with his sister for a year or two while running SR) to the undercover FBI agent. Yes, bank wires, not bitcoins. Since banks offer essentially zero security, it's very plausible his true name was on it and everything after that was just filling in the details as they investigated 'so who is this Ulbricht guy anyway?'
(These sort of leaks are always much easier to find in hindsight: no one ever noted the Shroomery or Bitcointalk or Stackoverflow leaks before the indictment was released, yet once you knew what you were looking for, you could find the posts in minutes.)
Choose your own adventure:
a) He got to learn from his mistake.
b) That incident was recounted years later in the criminal indictment.