Humans are good at pattern recognition. But we see patterns based on personal experience and things that are close and familiar. This is called confirmation bias because that act of recognition typically confirms what we already believe. See also: Confirmation Bias in Foresight: Scanning to Find What You Already Believe. That is the biggest and most routine bias in observing change. It's more an instinct and even if people know better, they lapse into thinking that way.
There is no "everybody"
A great example is our assumptions about Millennials. It's common to see them as tech-savvy, urban, Starbucks-frequenting, plaid-wearing, indie-band-listening. That stereotype is a shorthand we use for understanding and explaining them, but it's dangerously narrow. It has been fixed in our heads and gets reinforced all the time. Then we look for it in the world and say to ourselves, "there's another one".
In fact, we base much of our view of the Millennials on what is a few percent, total, of people born 1980 to 2000. There is no "they all" you can lump together. What's everyone else born between 1980 and 2000 doing?
The same is true for Baby Boomers, Gen X, Hispanics, immigrants, Republicans, etc. etc. There is no everybody.
What to do about it
1. Check yourself. To understand the world and how it's changing better, examine your assumptions about what's going on. Assess your biases and face them. Write them down, say them out loud. Say, "of course I am biased because I am _________."
2. Step away from your worldview. Do what you can to deepen your understanding of others. This means getting past stereotypes, and wholesale categories. Read and view stories told in others' voices. Talk to strangers. Listen.
3. Walk a mile in another's shoes. Immerse yourself in other communities where you can. Watch and listen. Read and view stories from diverse viewpoints. Follow Instagram or photoblogs from places and cultures and groups far and far different from you. Think of someone quite unlike you. Then, look at things with those different eyes. For example, if you are exploring change for a consumer product, go to a store that sells products like that, "wearing" a different persona. What would that person see and care about? You can't get 100% there, but you will move off the safe zone of things that are familiar and comfortable to you.
4. Be ready to be wrong. Assume your conclusions will often be wrong. This means, despite your hard work at trying to transcend your biases, assume you won't get there every time. Knowing you might be biased will protect you from relying too much on your "certainty" about what's true.
Take these steps and you'll stop just confirming what you think you know. You will start knowing new things.
Another post: Talk to the Frog, has a parable to tell that relates to this post.