You can typically reapply for an F1 visa if your first application is denied, but you will have to start the application procedure over. The SEVIS fee won't need to be paid again, but any applicable fees will need to be made twice. There are many reasons why F1 can be declined, the most common among them is, lack of financial proof, missing documents or errors in them, you are not able to prove your stay in the country, failure in a background check, failure in explaining your answers in an interview.