Three phases of matter and their transition

Examples: For over a thousand years, the going theory of “chemistry” in Europe was the theory of the four elements: the world is made of the four elements of Earth, Air, Fire, and Water. That is 100% wrong.

It is not 100% wrong, and the evidence of it  are rocks,  feathers and water.  Then, obviously, fire can convert between the three. I would call it a very workable theory until the instruments get better.
The question was: What is the most important knowledge? 

Feynman answered was the knowledge of particle interaction. That is likely the most useful information, it gets the new generation some better instruments and leads to mathematics. I would agree, but it is not the most fundamental.  The utility of a fermion and boson model is greatest. It is still not fundamental. Fundamental would be: We are limited to 3D measurements, but there is is a more granular separation between a set of finite universes. But that has little utility, it demands no actions.