Readers decide inside ten pages, and often inside three. That is not unfair; it is a workload reality. Your opening has to make a promise clear enough that continuing feels like the obvious choice.
Four jobs, all done by page ten: establish the tone accurately, make us care about someone specific, put a live question in front of us, and show the world's rules. Tone first — a reader who mis-reads the genre in the opening will judge everything after against the wrong standard.
The most common failure is setup before story. Pages of ordinary life 'so we understand her' are a bet that the reader will stay for information without tension. Interleave the setup with the disruption instead: we can learn who she is while she is already in trouble.
Page one has its own rule: something specific and concrete, on a page with breathing room. A dense block of world-building at the top of page one is the most reliable way to lose a reader who has forty scripts to get through.