To give two examples, sharing opinions and pieces of your life online was generally a confusing concept 15 years ago. Now it is considered a virtue by many and an important part of distinguishing oneself from their peers (or even a career in itself). Another one is new music being uncomfortable (although, of course, people would rather claim it's "bad") and in your face and that sentiment being shared by the majority. Until it "suddenly" isn't. Not because the music changed – it's a recording after all, frozen in time – but because it has changed us.