Find it by reading the ranking page against your own for the single load-bearing difference, not by running a tool’s content-gap list. The method is to sit with both pages side by side and ask what this page does that explains its win: the unique angle, the data or evidence it brings, the depth it reaches on one decisive sub-question, the format it uses, or the trust signal it carries. You are hunting for the one difference that matters, the gap that is actually holding you back, not cataloguing every feature one page has and the other lacks.
The reason to read rather than diff is that most gap analysis flattens the important difference into a long list of unimportant ones. A tool will tell you the competitor mentions twelve terms you do not, and bury the real cause among them. The decisive difference is rarely a count; it is usually qualitative, the page answers the underlying question more directly, or includes original data, or covers the one sub-topic searchers really came for in genuine depth. That is the kind of thing you only see by reading both pages as a searcher would, asking which one you would actually trust and which one finishes the job.
So the procedure is concrete. Open the ranking page and your own next to each other and read both fully against the searcher’s intent. Note where the winning page satisfies the query in a way yours does not: an angle you missed, a question you answered shallowly that it answered completely, evidence it has that you lack, a format that fits the intent better, or a credibility cue that makes it more believable. Then weigh those candidates and pick the one that most plausibly explains the gap, the load-bearing difference, rather than trying to close all of them at once.
To act on this, read the top page and yours side by side for the one decisive difference and commit to closing that gap specifically. Resist the urge to chase the full content-gap report; find the difference that actually matters and fix that, since it is the lever that moves your page rather than a list that scatters your effort.