Andrew looked at Barry and asked, "What big mistake? Tell me about it."
"What? You still don't know? Hurry up and Google it."
Barry took a deep breath and said, "The great mistake I once made—the Flashpoint Universe."
In the DC Universe, Flash, Barry, had once made a terrible mistake.
To save his mother, he went back in time to stop the Mastermind from killing her, rewriting the Timeline and creating the Flashpoint Universe.
Later, with Andrew and Diana's help, Barry tearfully stopped his former self and restored the Timeline to normal.
Andrew asked, "Did the other Barry also want to save his mother?"
"What Barry wouldn't?"
Barry sighed and said, "To be precise, he didn't just want to save his mother. He also wanted to save his father, just like I did back then."
"My mother was brutally murdered, and my father was accused of murder and kept in prison."
"I studied law so I could get my father out. In that respect, the other Barry and I are the same."
"However, the Barry in that world wasn't as lucky as I was. I met you, Mr. Wang, and my father was easily released from prison."
"That Barry had restoration footage sent by Batman, but it was nowhere near enough to prove his father's innocence."
"So, that Barry wanted to go back in time and save both his mother and father. The method was simple—he only had to put a can of tomatoes in his mother's shopping cart."
This was what happened: after Barry's mother got home, she realized she had forgotten to buy canned tomatoes and asked Barry's father to go out and get some. When he returned, he found his wife lying in a pool of blood. He became the prime suspect and was thrown into prison.