Overfitting (one word) is such an important concept that I decided to start discussing it very early in the book.
If we go through many practice questions for an exam, we may start to find ways to answer questions which have nothing to do with the subject material. For instance, given only five practice questions, we find that if there are two potato and one tomato in a question, the answer is always A, if there are one potato and three tomato in a question, the answer is always B, then we conclude this is always true and apply such theory later on even though the subject or answer may not be relevant to potatoes or tomatoes. Or even worse, you may memorize the answers for each question ...
