This approach was important for Justin because when he was in a tough situation with school he would maybe reminded himself all the ways he had failed and then it would get worse. Telling yourself all the was that you didn't succeed, won't help and you will fail over and over again unless you change you're mindset. This is what Justin probably did and that's why things have been harder for him.
Becky had everything come to her easily so when she failed her drivers test, she didn't feel so good. She started reminding herself of the ways she had "failed", but Justin didn't want her to make the same mistakes as he did. So, he told her that it won't be the end of the world if you fail because you will get another chance.
