the structure-property-processing-performance paradigm
This is the single big idea the whole subject rests on. Draw a tetrahedron (a triangular pyramid) with four corners: structure, properties, processing, and performance. The claim is that these four are locked together. A material's internal structure decides its properties; the processing you use sets that structure; and properties plus shape decide real-world performance. Move one corner and the others shift with it.
Walk through it with steel. Structure: how carbon atoms and iron crystals are arranged. Processing: heating steel red-hot then quenching it in water traps a hard, distorted structure (martensite), while slow cooling gives a soft one. Property: the quenched steel is hard but brittle, the slow-cooled one soft but tough. Performance: a file needs the hard structure, a car fender the tough one. Same chemical composition (iron plus about 0.8 percent carbon), opposite behavior, purely because processing set a different structure.
This paradigm is why a materials engineer never just looks up a fixed 'steel strength' - the same alloy can be several times stronger or weaker depending on how it was made. It also tells you where to intervene: to change a property, change the structure; to change the structure, change the processing. It is the map you will use for the rest of materials science.
1080 steel (0.8 percent carbon) water-quenched becomes glass-hard and brittle; the identical steel cooled slowly in the furnace becomes soft and bendable. Composition unchanged - only the processing, and therefore the structure, differs.
Same atoms, opposite behavior - processing sets structure, structure sets properties.
The link runs mostly one way in practice: you control processing, which controls structure, which controls properties and performance. You rarely dial in a property directly - you engineer the structure that produces it.