In a school, a student went through a class, reading the textbook and studying all the notes; and received the highest marks possible on their examinations.
They had a thorough knowledge of the subject.
One of their friends had a younger sibling who was slated to take the same class.
Their friend, knowing that they had already taken the class and done well in it, asked them if they would give their brother the notes that they had taken.
Since they had already done the hard work, the younger brother would have an easier time in the class by knowing what to do and what not to do upfront.
The student obliged with no objection and gave their friend the notes to give to their younger brother.
About halfway through the class the friend came up to the student, telling them of how their younger brother was struggling in the class.
“I thought you did well in the class?”
“How can it be that my brother is failing with your notes?”
The student responded:
“It is probably because they have my notes.”
“Where are theirs?”