I think, it is true, that sometimes people can be bad students at their schooltime but after they can become successful in life.
The main reason of this case is personal skills that bad students can have. For example, the ability to defend your point of view or resourcefulness are important for different life’s cases. These qualities help people to manage with a lot of emergency situations. But excellent students can have other skills like patience and carefulness. It is less important for real life experience in the modern world, for this reason bad students now can have large benefit for their lives. A lot of famous people, such as Donald Trump or Steve Jobs, did not have cool grades and big achievements in school, but they have become really successful persons now because of their individual qualities.
But sometimes, this rule does not work clearly. A lot of students which had good marks in school can be successful. Unlike bag students, these students have a lot of knowledge in different fields. They can use deep knowledge in biology, math, physic or chemistry for handle so difficult cases in real life. Also, it can be useful for many professions such as a doctor, an engineer or scientist. Many fields require fundamental knowledge and it cannot be replaced by any soft skills. It is easier to be great professor or scientist when person have good education base. For example, my grandfather had excellent math and physic grades in school and in his adulthood, he becomes great engineer.