While two of the wonderful things about physics are the universality of many of its theories and the way we can understand more about a system by digging deeper and understanding how its parts relate to the whole, it is also true that we often have to choose the most appropriate theory depending on the scale we are interested in. If you want to fix your washing machine, you do not need to understand the intricacies of the Standard Model of particle physics—even though washing machines, like everything else in the world, are ultimately made up of quarks and electrons.
