Which is that one book on Design/UX/IxD/Usability/etc etc that you
will like to gift to your engineering folks in management as a new
year gift that will make them understand its need and value. On
similar lines which is that one book that you will like to gift the
hands-on engineering folks to make them understand that thinking about
user needs is equally important as thinking about the algorithms.
Mind you only one book for each that will create the maximum impact on
their thought process :-)