When we're deep in our writing, we don't tend to notice these words slipping into each paragraph as we write. Even on rereading, they might not jump out to us because the rhythm of each line just makes sense in our own head.
Do you even see it?
It is only when someone brings these words to our attention that they shine out at us like some great ugly beacon.
This is especially true with our repetitive phrases. Often in drafting, so much time has passed since you last wrote in a character's anger that we reach for the same descriptor. Having written it, we might lack the association. But the second a reader recognises a repeated phrase, it'll jump out brighter and brighter each time they encounter it.
You should also consider your format. Audiobooks can highlight the phenomena even more so than books. In one audiobook I listened to everything happened "at speed", and every time it did I sighed.
We don't want our reader sighing every time there is a particular action or emotion!
Borrow some eyes
Do not despair! There are some very simple solutions to this. A second pair of eyes on your work will bring all the clarity you need. This best comes in the form of a beta reader. When you work with a line editor, they will deal with all the repetitive words and phrases. But it doesn't hurt to get your manuscript in its best possible shape on your own steam (and the community steam of beta readers).
The person you ask to read over your work will approach it with none of the context or expectations that you do. Without the same innate connection to the rhythm of your sentences, your second pair of eyes will run into each and every repeated word.
Writing is a community activity
A beta reader is a really good place to start for flagging up repetitive words. You can take part in a manuscript swap within your writing group or hire someone to take a look for you.
If you're in a writing community, you are already surrounded with people who could beta read your work. Manuscript swaps are a great way to support each other through the self-editing process. If you're not already in a writing community, find one! There are online and in person communities of all sizes, locations and genres. Start your search at your local library or have a click about online.
Remember, beta readers are not mind readers! When you work with beta readers, make sure you task them to look out for repetitive words so that they can help you where you need it.
Alternatively, many editors offer beta reading as a service. The benefit of this is that you have a clearer idea of the timeframe and can be certain that you'll get the feedback that you're after. It is also a good option if you are worried about how feedback with be communicated. As well as being trained in writing craft, editors will definitely know how to communicate criticism in a way that is kind and constructive.
Now you know what your pesky word is, you can self-edit with confidence. Do this with care. The answer is not usually to delete every single instance. As you work through, consider its usage in each and every instance. Think about the impact of the words, the effect you want it to have on the reader and the message you want it to carry. Make your changes accordingly.
But half the battle is knowing that they are there!