How do people do hard hard math and science?

Answer 1

Learning the basics of any subject requires effort. Some subjects have a logical progression others do not.
Mathematics, a requirement for all other subjects, is fortunately the subject that demonstrates this property most vividly.
It is similar to learning how to crawl, then walk, then run.
Most people can learn how to do each of these things. However some people are better at it than others. Usain Bolt can run better than most people on the planet because he has a talent for it but mainly because he works extremely hard to better that talent.
It is the same with academic subjects. Each of us can learn the basics but some have a talent for certain things and some of us work extremely hard to improve that talent.

Answer 2

People are different. What you might find hard hard in mathematics or science other people might find easy. But there will probably be other things that they find hard but comes easily to you.

It is easier to do what seems to be hard if you understand what you are required to do rather than simply follow the "rules". Proper understanding takes time and effort but, in the long run, is well worth it.