A successful F1 visa applicant will have several very strong reasons to study that specific subject, and he will be able to elucidate those reasons clearly, calmly, and in detail.
He will be able to explain why he needs to study in the US rather than in his own country or a closer and less expensive one, such as India.
He will be able to discuss the subject with a consular officer who might well have some knowledge about it. He will know what research and progress is currently being done, and what it means.
He will be able to describe exactly how his studies will be paid for, without using up the entire family’s financial resources.
He will be able to explain precisely how he intends to use the knowledge that the studies (not just the degree) will give him when he returns to his own country, in order to have a far more successful career (and life) than he would have had he not studied in the US.