Many people have not taken advanced math or advanced science. They think education is all about teaching. However, it is a mistake to believe that a smarter or more accomplished professor will be able to teach all students.
In math, people hit a learning wall. They are unable to master a foundational level of math and cannot proceed to higher levels. This could happen with multiplication, algebra, geometry, calculus or some higher levels of calculus. They could also master the prior levels but are just unable to understand the next level.
A student can be sitting in a fourth-year math class and they were doing great up to that point. Suddenly, new topics come up and the student can no longer get it. The new topics require the ability to visualize something and they cannot do it. The professor will put up new equations and provide some discussion of the principles. Other students will understand but some will be unable to get it.
You thought you were good at math and it was going to be part of your career. The lesson is that you were wrong. You can be a well-paid life insurance actuary or you can find productive work in finance. However, advanced math is now done.
Why not ask for some private sessions with the professor? The professor breezed through this level of math and went onto five levels beyond. He cannot debug your problems with it because he never had those problems. He probably did not successfully help other students with those problems either. The other students dropped the classes and realized it was over.
How about using tools like calculators, spreadsheets and computer programs? This can help with certain problems. It is possible that someone could train themselves through visualization issues.
However, if you are using crutches you will not be able to keep up with a recreational runner. You will not keep pace with a college athlete.
Many people use spreadsheets for statistics. The functions are like black boxes. They are putting in inputs and answers are coming out. The workings of the functions are a mystery.
Higher education in math, science, and medicine is doing some teaching but it is doing a lot more selection.
Modifications and Caveats
There have been comments which correctly point out modifications and caveats are needed.
Many teachers at high school and through universities are not competent. It looks the student cannot learn when it is the teachers.
In Universities, there are professors who are famous for research but are unable to teach. There are others who are able to teach. There should be separate careers for lecturers and researchers.
Math, science and other subjects are very broad. You need to parse where you are really hitting a wall and the size and impact of the problem area.
Einstein was not a natural at differential calculus. Einstein was not strong at graphing or rendering complex equations.
Great artists of the past need not have been great at all aspects of art. The Impressionists may not have been able to match Vermeer for realism, but they had other contributions to make.
However, Just because Mugsy Bogues and Spud Webb exist as short pro basketball players, do not convince yourself that you will also be the exception and also make it the NBA. This would apply to academic pursuits as well.
Thanks to the commenters for adding the needed specification.