To be fluent in a language means not only that you can understand it, but that you can speak it competently. Competency in the language does not necessarily make it your first language. It may be your second, or third. Your first language is your dominant one.
Reason can be thought of like a language, so can emotion. Emotions can lack reason, and reason can lack emotion. Often, one dominates, the other is afterthought.
“Reason and the ability to use it are two separate skills.”— Franz Grillparzer