Ph.D. thesis is always a qualifying work. You defend some work in which you show your qualifications. This does not necessarily have to be some kind of breakthrough direction in science, practice. But sometimes this concept – qualification work – is somehow simplified. It is believed that if you have written several formulas or 150 pages of reasoning, the qualification work is ready and you can go to defend it. However, it is not. In any case, a Ph.D. thesis should contain at least a new look at some well-known problem statements or some new solutions.