In what way did einstein question his own scientific achievements?

Since I don't know the context of this question, I'll answer it the way a scientist would.
We know that Einstein was a scientist. Scientists are always asking questions and creating tests to solve problems. Einstein most likely didn't view his achievements as the answer to the problems of the universe. He probably saw a lot of flaws in his work. Even if he didn't, a true scientist is always questioning things. The definition of a scientific law is a theory that has never been proven false. He probably wanted to know if his achievements were theories or if they were laws.
These are just a few ideas. Take a minute to think about the context of the question and what you think that the answer should be based on that.