There are some researchers who take on projects that expose the limitations or gaps in previous studies. It is quite hard to find a completely original topic of research especially when so much work has been done in science already and so much work continues to be done. But every project has some gaps or some point that can be explored further or examined in a different way, which is where many researchers get their project ideas from.
So, what do researchers do when they are looking to continue work on an existing theory? They first examine what are the resources at their disposal. What project can they take up? There is no point in taking up work that the researcher later finds that he has neither the money nor the tools to handle. Therefore, it is essential that the researcher handle bodies of work that can be completed successfully.
The researcher then has to find all the literature on the subject that he is interested in. He has to look within himself and find out what piqued him about the previous body of work in the first place. Every book ever written on the subject, every manuscript ever printed and every paragraph ever documented on the topic should be read and internalised.
Then the researcher should start looking at loopholes in the old research and the findings that he does not quite agree with. This will give him an ideal starting point for beginning his own project. When he is reading through the old material, he should be mentally forming a hypothesis of what the end result should look like. What are the tools that the previous researcher used, and which ones were not used? This question will direct him towards the material that he should be collecting for his work. Once he has assembled all the literature and material, he can start his work.