Lu You (Southern Song Dynasty), an ancient man, learned nothing and died for a long time.
What you get on paper is so shallow that you never know what you have to do. The first two sentences should be used to educate sons to persevere, which means that the ancients always tried their best to study and were willing to work hard when they were young. So stick to it. The last two sentences emphasize practice, apply what you have learned, and focus on practice.