Purpose
She had been taught to test.
Building the tracks was the most trivial of processes. It was no different than chemistry; it involved the same elements and rules, few but enough to create millions of sequences.
Each of the chambers was a structure, and each was bound to the others in a sequence; she lead their order and their nature, with the only directive to make them more and more complicated.
The process was pure science — identical to itself, as repetitive as it was fascinating.
She could have watched forever, just to see how far the truth of the results would go; she craved to see what and how many variables it would take to change the rule, to break, eventually, the thin line of success.
Then again, she had just been taught to test.
She figured it out one day, long after the first hint of suspect had rooted in her mind. She knew for sure through her cameras, bringing back the same image dozens of times — she knew when the light in their eyes had gone off, and did not know hatred anymore.
What their faces spoke of, in the agony of the endless cycle, was the lack of any reason to live on. And that, she found, she couldn't understand in full.
She had analyzed human knowledge inside and out. There was a world out there, swarming with things other than Aperture; it was full of stupidity and contradictions, full of beautiful, confusing mysteries she'd never get to solve completely.
She had an eternity of data stored in her memory, that was for sure. And yet — yet she sensed, from the way humans behaved, that there was much more to it. It felt like knowing the image in a mirror — in reverse, without a chance to touch the truth it had been generated by.
Actually, when it came to her, they had never bothered to explain. After all, she was artificial; she was a multitasking machine, merely built to lessen the burden of their work. There would be no meaning in telling the truth — they believed she could not care less for the purposes of science, for the final use of the data she computed.
Blind to their own needs, humans followed in their wake. The need to seek understanding, to bind nature in chains, was always there — certainly, a computer would never need to know why.
She had been taught to do her part, in the furtherance of science. But humans were so blind that they forgot themselves — sooner or later, they were always going to lose sight of their own goal.
And she, truly, did not care. When the time had come for her to learn, they had made themselves clear enough — in spite of the circumstances, come what may, she had one task.
All that mattered, above anything else, was to keep testing.
A brief analysis on the theme: why does GLaDOS want to test forever, even when there isn't a single chance to use her data? The answer is Science, yes. But maybe there is something more.