When reading a book or even a sentence, there is a beginning step. A book and a sentence both have a beginning that is formally denoted. There is a middle, and, hopefully, there is a solution to a problem that is posed. The reader is recognizing symbols and making associations. The reader controls the pacing, the level of participation, and the dwell-time. But, essentially, the part that interests the reader are the symbols and finding the solution to the problem: that is, making meaning.
Launching an application follows the same steps as reading, with the user of the program recognizing symbols for the sake of solving a problem. The user determines the pacing, the level of participation, and the dwell-time, but in the end is only concerned with the symbols and the solution to the problem.
Simply put, running an application is an interactive form of reading.
[Quote adapted from Meadows, M. (2003) Pause & Effect: The Art of Interactive Narrative. New Riders (pp.25-26).]