Why Does Anyone need 6 Copies of the Same Subject?

 So in cleaning out my collection of technical books, I have come across 6 copies of books on the subject of Compiler Design.  Somewhere back in the recesses of my mind I can remember having perused through all 6 volumes, but not reading any one of them from cover to cover.  I read as much as I needed to understand the topic and then use what I learned to complete the task at work.  It fit my "Renaissance Man" motif that I was trying to accomplish, while being able to meet the challenges of the task at hand.

I have found over time that I am much more effective when I have just as much as I need of a subject without being a master in the subject.  I use all of this cross knowledge of topics to glean out a reasonable approach to accomplishing a solution to a problem.  In the case of these 6 books, I was able to construct a computer language and module for teaching repair techniques in a computer based trainer.