Each piece informs how it fits with other pieces. Pieces mesh into sections. Sections eventually join to show the whole picture. The analogy comes full circle by substituting scientific facts for puzzle pieces. Pieces represent evidential facts.
Scientific understanding relates one fact to others.
Physics principles enable a systematic arranging of the diagrams into a hierarchy to represent what physics is all about the structure of reality. The structure defines how everything interrelates. But, it did not immediately answer all questions. The big questions of philosophy and science are answerable only when the structure of reality is reexamined through the lens of other disciplines. Multidisciplinary research produced a categorical understanding of everything.