The distinction between fluid and crystallized intelligence is important because the two are influenced by different factors. While the former is more biologically determined and genetically predisposed, the latter is shaped more by experience. This is a little bit similar to what we know of sports: some people are more likely to develop stronger muscles than others, but this does not turn them automatically into world-class athletes. Instead, they need many years of training and experience to make it to the top. Likewise, people need to apply their fluid intelligence to a particular domain of knowledge, such as physics or history or neuroscience, to become really good at what they are doing.
When it comes to cognition, psychologists speak of a two-component model of cognitive development. By that, they mean that cognition is always a combination of some aspects of fluid intelligence and some aspects of crystallized intelligence, but the two components develop differently across the lifespan. After you are born, your body and brain develop and you become smarter without much effort.

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