Admittedly, beginners could contribute to some important discoveries because their thought might not be confined by existed thinking patterns. To research on a specific discipline, beginner is regarded as freshmen to some extent. Though the lack of experience may hinder them to acquire further progress, on the other hand, this may be an opportunity for them to think and research in ways different with mainstream methods. For example, Einstein, his distinguished Theory of Relativity was created only through he takes another way against the dominated theory constructed by Newton. The birth of such a break came from a beginner but not experts.
However, experts have much experience which is one of the most important factors to the birth of great discoveries. As we know, a building could be constructed only after the basement is founded. Experts are people who research in a specific area of discipline, they know the previous and nowadays, theories, data and trends in this area clearly, which can help them to make progress in objects they engaged in. Newton, a famous scientist, made many great discoveries in physics. What he said about his achievement is that only he stands the shoulder of giants so he can see further. This is the best generalization why discoveries are made by experts.
Furthermore, most of research on many fields is a time-consuming and rigorous works and call s for persons who devote all his time and energy on them. Common sense told us that it usually takes a person many years to make a discovery. That is an energy-consuming work.