Personas

Through creation and simulation of various personas a service developer can quickly imagine scenarios where different people may experience a certain service without performing real-life tests.

Additional reading
Holtzblatt, Karen, Jessamyn Burns Wendell, and Shelley Wood. Rapid contextual design: a how-to guide to key techniques for user-centered design. Elsevier, 2004.

Cooper, Alan, Robert Reimann, and David Cronin. About face 3: the essentials of interaction design. John Wiley & Sons, 2007.