Which sentence in this excerpt from Nathan's memoir, "The Big Race," shows the writer’s reflection on his experiences?
First, I started by jogging for three hours every day. Next, I tried to find as much information as possible on how to run a race. I talked to my coach and friends. They taught me how to lean forward in the correct manner, how to maintain the correct posture, and most importantly, how to increase my strength. At first after running just half a mile, my heart would start pounding in my chest. I could run no more than half a mile. A lot of times I felt like just giving up, but I kept right at it. I even changed my diet and became more conscious about eating food that would make me strong and healthy. I increased my intake of fresh, raw leafy vegetables. Finally, in about four months, I was able to run three miles without tiring out.