With respect to search advertising (and SEO as well) a common mistake I see made is business owners not understanding that a word or phrase which you think should be indicative of a good fit might mean something totally different to the person making the search ... in other words there is a disconnect between your interpretation of some kind of modifier/qualifier that you think means your search ads are reaching the right audience, and what the people 'behind the keyboard' making the search actually think.
Take the word "commercial" as an example.
Let's say your business provides cleaning services to organisations of a certain size that you define as 'commercial'.
In your internal context, your business might interpret a "commercial" prospect as being an organisation of a certain size (whether based on revenue, headcount or whatever).
So you go on over to Google Ads and set up a campaign targeting prospective customers searching for 'commercial cleaning services' ... because putting the word commercial in there means you'll only get the right kind of people searching!
You get ad impressions, you get clicks, conversion tracking tells you you're getting leads ... but the leads you're getting aren't a good fit. Most of them are too small, poorly qualified and so on (I see this same scenario play out over and over again).
But how could this be if you've set your ads to only show if the user's search directly references 'commercial cleaning'?
Google's increasing proclivity to straight up ignore your targeting aside (more on that another time) there's every chance that the people who did search 'commercial cleaning services', clicked your ads and requested more info thought they were commercial because their definition of commercial is that they have a small office or retail unit that they want to have cleaned (whereas you were thinking more multi-level office buildings or larger premises).
There's a deeper consideration in this that - as a rule - the larger the organisation you need to reach the less likely the buyers/influencers within said organisations will just jump on Google and search for a solution (as a rule they will often have a 'mental map' of vendors prior to starting the purchasing process) but once again that's a topic for another day.
For now, it's worth considering (particularly if you find yourself in the scenario where your keyword targeting for paid and/or organic search "looks right" but the commercial reality in terms of leads says otherwise) if your interpretation of a particular keyword or phrase too narrow compared to the meaning it could convey, or whether it is appropriate at all.