I think Joel Spolsky had a nice spin on this a few years back:
"Once you've written a subroutine, you can call it as often as you want. This means that almost everything we do as software developers is something that has never been done before. This is very different than what construction workers do. Herman the Handyman, who just installed a tile floor for me, has probably installed hundreds of tile floors. He has to keep installing tile floors again and again as long as new tile floors are needed. We in the software industry would have long since written a Tile Floor Template Library (TFTL) and generating new tile floors would be trivial."
"Once you've written a subroutine, you can call it as often as you want. This means that almost everything we do as software developers is something that has never been done before. This is very different than what construction workers do. Herman the Handyman, who just installed a tile floor for me, has probably installed hundreds of tile floors. He has to keep installing tile floors again and again as long as new tile floors are needed. We in the software industry would have long since written a Tile Floor Template Library (TFTL) and generating new tile floors would be trivial."
http://www.joelonsoftware.com/news/fog0000000337.html