Sometimes I encounters with the word ‘holistic’ around, and most, if not all, of those times, the quality of the work the word is being used in is usually poor. Holistic explanations also abound: they talk about interconectedness, the importance of the relation between parts above and beyond them, and so on. In more serious work, holistic-like explanations can be found in reference to ’emergence’ or ‘spontaneous behaviour’.
The problem with the attitude of refusing to analyse the parts of a particular system and to consider only the system as a whole is that you can’t really get to fully understand the system: you miss information. You can say that everything affects everything, and surely it does: I have mass, so I exert a force in your body, wherever you are in Earth. But how strong is that force? How relevant are those relations? One can claim both that everything is related with everything, and at the same time say that the relationships are not of the same type or strength. That is, one can really open the black box and reduce the system to its parts.
There is a philosophical mistake powering holism, and that is the belief in emergence: to think properties that are not present in the parts of the system or its governing laws can arise. Saying like the wetness of the water cannot be analysed in terms of individual atoms, that you need a lot of them to have wetness.
That is wrong because if you have a system governed by laws, the behaviour of said system is already set by said laws. Causality runs in one direction, not in the reverse: The system does not cause properties in the parts, it is the other way around.
In the example of water, wetness does not emerge: wetness is just a result of the composition of water together with the laws of physics. One water molecule has as much wetness as a the water in glass of water, only that intuitively you can imagine something being wet by the water in a glass of water, and not someting being wet by a single mollecule. You just need to think clearly about what you are meaning by wetness, and see how it is really not that weird for a mollecule to wet a surface as a liquid does. Think of the forces and interactions involved when there are lots of water, then work your way down to the molecule.
A related mistake is to think that because the degree of understanding differs depending on how you picture a system, views that provide less understanding also lack some properties the best view has. Take an airplane. One view is to see it as a whole: As a tube of aluminium with jet engines. Other view is to see it as a bunch of atoms. The first view helps us understand, design, use, airplanes, while the second is mostly useless. Therefore, the argument goes, the airplane has to be understood in the former way, and it is more than a bunch of atoms. The error here is that reality having a single basis does not mean we can’t see or model it through different lenses: We can talk about atoms, molecules, compounds, individual parts and the entire system. None of these ways of describing a system are wrong in the sense that they don’t describe reality. They are all referring to the same underlying thing.
A related reading is Huemer’s The Philosophical Complaint Against Emergence (1992).