Why should we value the memory of experiences? For me, it's simply because I enjoy them. It gives me momentary pleasure to think back on good times. But it also gives me momentary pleasure to eat ice cream. The tyranny Kahneman refers to is our bias towards optimizing an experience for the memories it will give versus optimizing an experience for the momentary pleasure of the experience itself. If memories give relatively little total future pleasure in comparison to the momentary experience itself then I think we are mistaken to optimize in this fashion.