Research is like a jigsaw puzzle

As a researcher, you have to peruse multiple historical materials, discover issues no one has discussed before, and prove their validity. Here lies the very pleasure of research. It is like creating a jigsaw puzzle within your mind. A historical record constitutes one piece. You consistently (and objectively) put pieces together until they form a complete picture.
Unlike a puzzle, however, the pieces do not come in a box — you have to search for them. Furthermore, choosing only those pieces that suit you will result in an overly subjective, skewed picture, so you must make efforts to remain objective (by backing your theory with actual proof). In order to achieve this, you must acquire more and more historical materials, approach them with an open mind, investigate them from various angles and interpret them as objectively as possible. Even the materials you personally find hard to understand might be indispensable in reconstructing images of history.
There are particularly many materials related to the history of modern and contemporary Japan. In fact, they come in such great numbers that lots of those sources have never been used by historians. To find and identify such materials (or pieces of jigsaw puzzle), and then make something new out of them is also a part of the fun.