It's a more common problem than it seems: two, three or more pages on the same website trying to rank for the same keyword, with none of them ever quite taking off. This is called cannibalization, and it often goes unnoticed because, at first glance, everything looks fine.
Why it happens
It's usually down to content created without a clear plan: a blog post and a service page talking about the same thing, or several posts on a very similar topic published at different times without checking what already existed. Each page tries to rank for the same search on its own, and Google, unsure which one to show, ends up splitting relevance across all of them instead of concentrating it in one.
How to spot it
The clearest sign is seeing, in Search Console, two different URLs from your site appearing for the same query in different weeks, alternating without either one settling into a stable position. Another clue is simply searching your target keyword on Google and finding more than one of your own pages in the results.
How to fix it
You rarely need to delete content. The usual approach is to pick the page that best answers the search and reinforce it, while redirecting the rest toward related but distinct variants, or merging the weaker content into the main page with a 301 redirect.
How to avoid it going forward
The root cause is almost always the same: publishing content without first checking what pages already exist on that topic. Keeping a simple list of which target keyword each page owns stops two different pieces of content from accidentally pointing at the same thing.
Frequently asked questions
Does keyword cannibalization directly penalise a website?
It's not a penalty in the strict sense, but it is an efficiency problem: instead of one strong page, you have several weak ones competing with each other, which usually translates into worse rankings for all of them.
How do I know which page should remain the main one?
Usually the one with the best current performance, the most internal and external links, or the one that most fully answers the real search intent behind that keyword.
Is this a common problem on small websites?
Yes, even though it's thought of as something that only happens on large sites. Just two similar blog posts, or a service page and an article covering the same ground, are enough for this problem to show up.