This is your brain on languages.

The image you see here is a visualization (which is obviously not comprehensive) of how a given piece of information in a language might get lodged into your brain. The piece of information could be anything: a vocabulary word, a grammar rule, pronunciation, a character, etc.

Every one of those lines emanating from the piece of information connects with one kind of exposure. The more exposures you get, the more connections your brain draws to that piece of information. The more repetitions of a given kind of exposure, the stronger that exposure becomes (imagine the lines getting thicker with each exposure). The stronger and more plentiful your exposures are, the more likely you are to remember the piece of information.

Exposure to a language can be largely divided into reading, listening, writing, and speaking. It doesn't matter if an exposure is via reading/listening (i.e., input from an external source) or writing/speaking (i.e, output to an external target). These traditional ideas of "output" and "input" are both input as far as your brain is concerned.

Output is input.