What makes a novel "a classic"? Discuss.

A novel becomes "a classic", when it is read over and over again generation after generation.  A classic novel must be unique and have the ability to leave a great impact on the mind of the readers.  By leaving a deep and significant impression on the mind of a reader, a book is able to plant its seeds for future generations.  The older generation, when asked by the newer generation for books to read, will no doubt recommend the "classic" if it held a significant impact on the mind of the individual.  In order for a novel to become "a classic", it must also be a good read.  This is a must because if the novel wasn't good, people wouldn't read it to begin with.  An example of "a classic" is To Kill a Mockingbird.  It's idea is unique, and it is also a valuable read.