In Chapter 12, Darry and Pony get into their fourth argument of the week concerning Ponyboy's grades. Pony yells back at Darry and asks Darry why he's sweating him about schoolwork. Pony could care less about his grades anymore and tells Darry that he'll drop out and get a job like Soda. Darry responds by telling Ponyboy that he has the intelligence to get a scholarship and that he's been living in a vacuum. Darry is aware that Ponyboy's attitude has drastically changed since the deaths of Johnny and Dally, and says, "you don't just stop living because you lose someone" (Hinton 148). Darry is encouraging Ponyboy not to fall into an apathetic state where he feels sorry for himself. He urges Ponyboy to live his life and not stop trying to accomplish his goals. Darry realizes that losing two close friends is traumatic, but understands the importance of being mentally tough enough to push through difficult moments in life. There is nothing that Ponyboy can do that will bring back Johnny and Dally, but the one thing Pony can control is how he chooses to respond to the adversity. Darry is essentially encouraging his brother to refocus and continue trying his best at life.
Darry means you have to go on with your life. Losing someone is difficult, but a person cannot just quit living when he/she loses someone who is close to him/her. Life does go on, and we have to accept what happens and continue to live our own lives. If we don't, what is our alternative? The only other thing to do would be to give up. Darry wants Ponyboy to realize that even though Johnny is gone, he has his whole life ahead of him, and he must continue to live it. That's what Johnny would have wanted him to do.
That meant that if you lose someone special or love one in your life you don't just die because of him or her dying. He is talking about losing Dally & Johnny.