It would be redundant to say a writer must also be a watcher. In many of my stories, the narrator is just that. In order for a reader to trust a narrator is for them to be believably observant. The level of observance is dependant on the character.
A four-year old narrator would be able to notice the name-brands of the furniture and products of his house.
A cat narrator won't be able to notice signs and writing.
However, an omniscient narrator is able to see and know everything. And, an author should be able to observe everything they encounter and know what should be mentioned and what shouldn't.
Here are some fun questions to answer.
When you put on your shoes, which foot do you pick up first?
Do you put your seat belt on before or after you turn on the car?
On which television channel is your TV when you turn it on?
What website do you go to first when you surf the web?
Do you fold paper hambuger style or hot dog style?
Remember, narrators should be limited, but author must observe everything.