Failure at DV visa Interview used to happen when the applicants don't meet the required eligibility or fail to provide the required documents. Lot of diversity visa lottery winners who had been selected used to lose their visas and their visa processing fees at their visa interviews every year. This used to happen due to their ignorance of the draw rules. Lot of people think winning the draw will allow them to get the American visas right away. But the truth is they have to apply for the visas using the online immigrant visa application form. Then have to wait for their interview date. On the interview date they must provide all the required papers and translations along with the Affidavit of support. All the eligible dependants too must attend the interview even if they are not willing to travel to America.
Millions of people used to participate in this DV Lottery program as it is a free to apply program and most of them didn't know about the rules and the procedures of the draw. Loy of people think that these American visas are being given to all the selected winners free of charge without any questions. Actually the DV lottery program is not a simple draw but it is covered with strict rules and regulations. If you don't read and respect them, you will lose the American entry permit along with your visa processing fees. Take note that there are only 50,000 entry permits available for any of the fiscal year program and normally 90,000 - 100,000 participants are being selected as winners.
Under this draw only submitting the entry form is free but if you are selected as a winner you will have to pay for the visa processing fees not only for you but for all of your dependant family members even if they are not intended to travel to USA with you.
Also there are some other expenses too must be met by the winner.
For to issue 50,000 American visas nearly 100,000 people will be selected as winners and will be asked to proceed with the winning under the normal immigration process to get one entry permit. So there is no guarantee that all the winners will be issued with the required entry permits or not. And the program is covered by closing date and time. Here are the main things that you will have to provide to the consular officer. By meeting all the eligibility and satisfying the interviewing visa officer is the only way to be issued with the USA entry permits.
Otherwise you will fail at the interview and the application will be rejected.
So these are some of the important things that can make a winner to be rejected at the time of the interview. It is important for you to read the current DV instructions carefully, before to start with the visa processing. Also you must read about the newly introduced E.O of the Newly elected American President's office.
Paid visa processing fee is also lost as it is a non refundable payment.
You can't re-apply nor can't complaint against their final decision anywhere.