Mine is more with changes in the world's (mostly the West's) perception of life. It's far more broad than one simple or small thing, but about changes with our Western society itself.
Decades ago it was there were no limits or the sky is the limit. Don't let others limit you, and if you work hard there are no limits to what you can do or what you can achieve. It was that feeling of hope.
Today, it's all about limits. You cannot do something or cannot break such and such a ceiling.
I suppose I should put it in D&D terms (as this is a forum). So, more of a parable that relates modern ideas to the old ideas. It's not necessarily D&D, but using D&D as a parable so people can sort of understand what I'm talking about in relation to society itself.
In older editions there was no limitations to the levels you could obtain. If you wanted to go crazy bonkers you could make a million level character (really out there, though I HAVE heard that some have played with characters with 700 or 800 level characters and such crazy stuff...but they could if they wanted to). You had this in 1e, and at the beginning of 2e (later they had stricter limitations to level 20, or 30 if High Level, or 40 if in the Forgotten Realms). In 3e and 3.5 there were no set limits on levels OR ability scores.
Fast forward to today, people are all about low bonded accuracy numbers (+4 spread between levels, not even a 10 point spread there), level 20 as the maximum level, and 20 being the highest your stats can ever be (though, admittedly, if you go with epic boons and such, you can get up to 30 in an ability score). It suddenly is all about limitations on things.
Off the D&D parable now...it's like people give up and accept that there are limits in life. It's like limiting hope. It's prevalent in society now. I don't get why people have this type of attitude and are promoting it these days in some places. You find it in music, TV shows, and other things. For example, even in a shorter term idea, in Doctor Who Companions like Rose and others were the ones that were ultimately the force of the universe in the final episodes that caused change. The doctor was there and effective, but in the end it was the companion that was the real thing. In more recent seasons it seems the Doctor is the effective force of change. There's a unwritten idea companions cannot be more powerful than the doctor. It's hard to see, but there (not as strongly as other things though). It's the idea that we cannot do things at times no matter how hard we try, or that we will never be as great as something else. It's like how superheroes are now the focus of our movies because normal people like you and I, we cannot accomplish the things those who are more than human have.