It's all interrelated

[Here is] a helpful analogy between linguists and medical doctors. The human body is a very complex system. Each part can affect the others in various ways, and a single symptom (e.g. a fever) can have several different underlying causes. Similarly, the grammar of a language is a very complex system. Just as the doctor looks for the diagnosis which will best account for the various symptoms, so the linguist tries to find the best “diagnosis” of the data, i.e. the hypothesis about the underlying patterns of the grammar that best accounts for the observable facts.—Analyzing Grammar, page 60

<idle musing>
And you can easily misdiagnose in both cases! So take heart, language students! At least in the case of grammar, you usually don't kill someone if you misdiagnose—although I once had a person try to conjugate a Latin noun and I almost died : )
</idle musing>