I've never defended a thesis. Do people actually fail?
No. Usually, a month before you present your thesis to a committee invited from other universities, you present your research to faculty from your department. If your work is weak, they recommend postponing your defense until the following semester (in six months). In Russia, there's a five-point system. And the grade you receive at your defense greatly influences your future. Your employers see it. This grade is taken into account when hiring research teams. And so on.
No. Usually, a month before you present your thesis to a committee invited from other universities, you present your research to faculty from your department. If your work is weak, they recommend postponing your defense until the following semester (in six months). In Russia, there's a five-point system. And the grade you receive at your defense greatly influences your future. Your employers see it. This grade is taken into account when hiring research teams. And so on.


