As libraries increasingly store books in off-site storage facilities or on-site automated retrieval systems, there is less capacity for library users to browse stack collections. This reduces the possibility for serendipitous discovery of books, or what the author refers to as a “collision with the collection”. This article discusses why this is happening and ways in which libraries can promote collisions with the collection even in a library world where books are less likely to be physical entities that are stored in traditional book stacks.