The Pragmatic Craftsman :: Simplicity from complexity ::

An investment in learning software engineering principles is a particular good investment for a software professional to make because that knowledge will last a whole career溶ot be half obsolete within three years.

As a software development professional, you need knowledge of specific technologies to do your job. But you need knowledge of software engineering principles to do your job well. A continuing pursuit of such knowledge is one mark of a true professional.