Rick conoce a Morty.
Boston 1974: Ex-boxer, salesman and occasional thief Stan Pines is down on his luck, when he sees a skinny scientist, Rick Sanchez start a bar fight, and finish it with fire. And for the first time in a long time, Stanford Pines laughs. Then runs, because the cops are coming and they might have warrant out for him.
Morty comes to the conclusion that everyone would be "better" without him. (Trigger warning: suicide.)
Some things can't be undone. Some things can never be changed. But that was a different time, a different life, and a different place. And Rick won't ever let it end that way again.