This metaphor refers to a person who has been ill for a long time. Usually, people know that he is ill. As long as there is a little problem and a little headache, he will go to the hospital at once. Such people will live a long life. The healthier people are, the less they pay attention to minor ailments, and the minor ailments will pass. In fact, this sometimes turns a minor illness into a serious illness, and when it breaks out, it is incurable. Especially at your grandfather's age, it is the physiological change of people. Maybe he is very strong at ordinary times, so he doesn't pay much attention to physical examination and doesn't know his illness in time. For example, diseases such as cancer, heart disease and cerebrovascular disease are usually invisible from the outside. Only through physical examination can we find out and take precautions in advance.