I said in the last post that the guy who was left by his girlfriend after what he did (he said he had done everything -- presumably good things in his view) was just not good enough for the girl. Well, if I were my student, I would have given that answer a B-minus. A better answer is: because the costs incurred during dating or pacaran are sunk.
Again, dating is a two-to-tango game. So, when the guy said he had given everything, chances are she had given everything, too. When they both were giving each other, they incurred both costs and benefits -- of which I do not want to dwell into details.
In the story (Samuel Mulia, my apologies, I'm using your article here again -- by the way, keep up good writing), one person is left out: the girl. The decision that is relevant to see why "she left me after all what I had done" is the girl's decision to leave him, not the guy's fate to be left alone. That is, what matters is what probably triggered the girl to leave. So let's focus on her.
In the period of dating, the girl incurred costs: makeups, fancy skirts, perfumes, even the effort to walk and talk "like a lady". All this she did to attract and later, to keep that lucky guy with her. Right before she did every single item above, she had an expectation: All these I would do because I expect him to give me this or that, in return. But once the activities were done (e.g. once the fancy skirt was bought), they all became sunk costs: they were not recoverable (well, she might go to second hand market selling the used skirt, but hey, she is a lady).
Fast forward. There was a quarrel between the two lovebirds. The girl was now at the margin of decision: leave or stay (or, if you don't like these terms, use: leave him or keep him). What would you think she had in mind, as factors affecting her decision? Yes the costs and benefits of leaving him. She would leave him if the resulting benefits (relief, chances to get a new guy, etc) exceeded the costs (effort to make him go and to make up good, convincing story to friends, etc). But the costs incurred during pacaran were not relevant anymore.
(If this is not convincing, try picture you are about to go mudik. You are thinking of driving your car or simply take the train. The amount of money you used when you bought the car is not relevant to your decision).
So, ladies, next time a jerk begs you to not leave him, using "Please don't go, Honey. Remember what I have given you all this time?" Tell him: "Baby, it's all sunk. Now shut up".