A word that appears twice in a sentence draws the eye both times, even if the
second appearance is not intentional. Reading aloud finds them.
The example
“The thing about writing is that writing is difficult, and the difficulty of
the thing is what makes it worth writing.”
Read aloud: writing, writing, writing. Three times in one sentence, and only the
first one was meant.
Why it happens
The thought has the word in it. The word comes naturally. The second use is
just how you think and you do not hear it when you read it silently because
your eye skips ahead.
The fix
Replace one. “The thing about writing is that it is difficult, and the
difficulty is what makes it worth doing.”
Or: “Writing is difficult. That is the thing. The difficulty is what makes it
worth doing.”
The word that should repeat
Sometimes a word repeats on purpose and it works. “The door was small. The
door was dark. The door would not open.”
This is deliberate. The repetition is a thing, not an accident.
The difference is that deliberate repetition has rhythm and accent. “The door
was small, dark, and locked” is rhythm. “The door was small, the darkness was
complete, the door stayed closed” is muddled.
How to tell the difference
Read it aloud. If the repetition sounds intentional, it is. If it sounds like
you did not notice, it is an accident.
Your ear is a better editor than your eyes.
The other case
A word that repeats at a distance: “The book was about a man who wanted to be
a writer, and the book showed how writing destroyed him.” The book appears
twice—once at the start and once in the middle. The distance makes the
repetition worse because the reader forgets they have seen it.
This one needs fixing every time.
Why this matters
A reader notices every repeated word, even if they do not consciously know it is
there. It reads as sloppy. The fix is usually just one word, and it makes the
difference between prose that works and prose that has mistakes in it.
The repeated word is the thing that editing finds when reading aloud that
proofreading will miss.