Targeting one keyword with two pages splits your own signals between them, which forces search engines to pick or rotate between the two, so each page underperforms what a single consolidated page would achieve. This is self-cannibalization, and the mechanism is direct: relevance, links, and engagement that should accumulate on one URL get divided across two, and neither reaches the strength it would have had alone. The instinct to “cover the keyword from two angles for more chances” gets the cause and effect backwards, because the two pages compete against each other before they ever compete with anyone else.
The split is what does the damage. When two pages on your site target the same query, the external links pointing at the topic land on different URLs, the internal links you build point in two directions, and the engagement signals fragment. Instead of one page concentrating all of that into a position it can defend, you have two diluted pages, each carrying half the case for why your site should rank. Search engines see two candidates for the same intent from one site and cannot give full credit to both, so the combined effort produces less than its parts.
The visible symptom is rotation and suppression. Google tends to surface only one of the two for the query, and which one it picks can shift over time, so the ranking is unstable and neither page holds a confident position. Often the page that ends up shown is not even the one you would have chosen, and the other sits idle, drawing effort with no return. Meanwhile you are maintaining, updating, and linking two competitors for a single slot, doubling the work for a worse outcome.
So the fix is to assign each keyword one clear page and let it own that intent. Pick the stronger page as the canonical home for the query, then consolidate the other into it or re-aim it at a genuinely different intent, redirecting cleanly if you retire a URL. One focused page collecting all the signals beats two diluted pages splitting them, every time, so stop running two horses in the same race.