Well, the answer is we don’t.
Yes, for common people, there is really no need to spend much time on thinking about some unrealistic philosophical questions. Are you the same person as who you were yesterday? Is the world your own world or is it shared by all other people? Well, getting the answer to these questions won’t make a single bit of difference in your daily life, not to mention that there probably won’t be an answer at all.
But some people do get fascinated in these questions.
Imagine you are using a computer and you want to calculate 13579 times 24680. You just need to know how to use the mouse, keyboard, and the Windows(or Mac) calculator application. You don’t bother to know how computers work internally. Why? Because you are busy. You have to work, you have to earn money so you can pay your rent and buy some food and have a good life. Your time is scarce and precious. Not all of us are Prince William or the son of Bill Gates. Even if you were, you probably would rather spend your time playing golf in Hawaii than learning some computer geek shit. Hey, I’m not saying this is bad or this is wrong. I’m saying the exact opposite. This is a wise decision for most people, I’d say. You do what you need to do, live a good life, and that’s more than enough.
I think philosophy is all about questioning what you see on the surface and trying to figure out what is actually happening underneath. Think about a farmer who lived thousands of years ago. He saw the sun rising up from the east and going down to the west every day. He wouldn’t be able to tell that the earth is actually orbiting the sun. Even if somehow he had known that, it would’ve had nothing to do with his life. He would still starve to death if, for example, he had a poor harvest. But does it mean that knowing the earth orbits the sun is meaningless? I wouldn’t say that.