Every person is a unique individual, even single-egged twins aren’t exactly the same. As you grow up, you learn new and different things which influence your interests and the choices you make in your life. These interests influence how you perceive the world around you, what gets your attention and what doesn’t.
The difference in this perception is a big issue for developers and designers. How can you make a program or object that suits everyone? This is something that’s impossible to decide by yourself, in order to find out whether your program is of any use, you’ll need to test it with other people in real-life situations. Sometimes this means that you’ll need to design different versions of your software for different (groups of) people.
The most common example of this is software being in different languages, but this difference could go further than just language. White cars reflect the most amount of light, thus meaning that they are cooler and easier to cool in hot countries, but harder to find in the snow in cold countries. Designing a practical and worldwide useful object suddenly becomes a lot harder!