Coding Horror: A Modest Proposal for the Copy and Paste School of Code Reuse
http://www.codinghorror.com/blog/archives/001257.html

Atwood, Jeff
Coding Horror
2009

Abstract:

If you use copy and paste while you're coding, you're probably committing a design error. Instead of copying code, move it into its own routine. Future modifications will be easier because you will need to modify the code in only one location.