Noam Chomsky, the father of modern linguistics, argues that learning languages is an unconscious process, and that our brains are pre-programmed to learn languages. Stephen Krashen in his famous 5 hypotheses explained that we learn  if we are exposed to language input that is (1) comprehensible (language that we can understand),  (2) highly interesting, (3) rich,  (4) in abundance, (5) challenging by 10% (i+1 hypothesis), while we pay attention, and in a very low anxiety environment. He calls this kind of language input "Optimal Input". So we are pre-programmed to learn any language, and that we need to feed it "Optimal Input."

Beniko Mason, a professor from Japan further studied Stephen Krashen's hypotheses, and did her own research while being a language teacher, and found out that a language learner needs to be exposed to 100 hours of language input over the span of 1 year to become an autonomous learner. It seems that after one year something clicks in our brains and the language starts to make sense.

Autonomy is important because the goal of language education is to lead the person to become an independent learner, which is a level where they can continue to grow in the language on their own without the support of a teacher.