Schengen refusal letters use numbered reason codes. The two most common in our practice are Reason 2 ('purpose and conditions of stay not justified') and Reason 3 ('information submitted regarding justification for the purpose and conditions of the intended stay was not reliable').
Reason 2 means the file did not clearly establish what you would do, where you would stay, or who would host you. Fix it by submitting a day-by-day itinerary with confirmed (not held) hotel bookings, return flight tickets, and a one-page cover letter explaining the trip.
Reason 3 is more serious. It means the consulate suspects fabricated or inconsistent documents. Common triggers: a sponsor letter without supporting bank evidence, hotel bookings later cancelled, employer letters that don't match LinkedIn or social media, or itinerary cities that don't match flight tickets.
Before reapplying for a Reason 3 refusal, audit every document. If a hotel booking was cancelled after the first application, get a fresh confirmed booking. If an employer letter was vague, get a new one with specifics. Never resubmit the same file, the consulate keeps records.
Wait at least 30 days, change at least 30% of the file (stronger financials, longer travel history, a new itinerary), and address the refusal reason head-on in a new cover letter. Most Reason 2 refusals approve on the second attempt, Reason 3 refusals approve on the third with a rebuilt file.