Or so the author hopes, because every time a reader has to stop and go back to check something, you risk losing them. Writing creates an imaginary world that the reader becomes immersed in so completely that they begin to believe that the characters are real, not imaginary.
The writer of the scene can picture it clearly in his or her head. They can hear the dialogue, so they write that down, they know how their viewpoint character feels so that gets included too. But they forget that the reader isn't there watching the scene in the way that the writer is, so they omit all the grounding details that create the scene. Instead it floats in space.
My first editor told me that the reader needs to be clearly told where and when a scene takes place - preferably in the first couple of lines of a scene, certainly within the first paragraph. After all, why keep it secret? Yes, it's good to show rather than tell, but there are somethings that really, it's easier/quicker/more sensible to simply tell.
Then the writer needs to add little reminders throughout of where the characters are - footsteps ringing out on the pavement, for example, or the honk of a bus, or smells wafting from a delightful cafe (or stagnant river).
Not only do those reminders help to anchor the scene, but they can provide useful character info. For example, in Kissing Mr Wrong, Briony and Lu are having a discussion about their respective relationships. That was originally a scene set in space (a lot of mine are, in the first draft). When I came back to it for the next draft, I had them walk down Milsom Street in Bath (a real place) and go into a (real) department store so Briony can make a purchase. While she's doing that, Lu tries on some make-up but doesn't buy anything because she can't afford it. What they try, what they buy, both grounds the scene physically but also shows the characters' different situations.
Trying to think of a final, closing para, it suddenly occurred to me - what about a scene actually set in space? All that floating in blackness. But then you'd have the stars around you, the crackle of the space suit mike, the sound of breathing, the lack of easy movement, the tug of the umbilical cord connecting you to the capsule/mother ship. See - even scenes set in space don't need to be written in empty space.