When I was a child my parents bought a table game called “travels in Europe”. The players had to travel through the map and to answer some geography questions to advance and travel more. My parents probably bought the game because they understood the principle of incidental learning.
What is incidental learning? (or accidental learning)
Incidental is defined in the dictionary as “occurring as a minor accompaniment” or “occurring by chance in connection with something else”. Therefore, incidental learning is learning that occurs as the by-product of another activity. In the case of my example, it was the side-effect of playing a game.
We can then distinguish incidental learning from deliberate learning. The latter takes place when we conduct an activity with the specific aim to learn something. So, learning European geography by reading a geography textbook would be deliberate learning while learning it by playing a table game would be incidental learning.
While learning a language is useful to know the difference between incidental and deliberate learning because it allows us to strategically plan our learning. I personally think that both can be useful and much depends also by what is the level of the language learner. However, I tend to use much more incidental learning because by doing so I learn German while watching an exciting movie, reading an interesting book, speaking with my girlfriend, and so on. However, deliberate learning can be particularly useful when we want to address a specific issue. For example, if I realize that there is a sense that I tend to use wrongly than I may decide to look at the grammar book and read what is the rule for that tense.
In sum, try to think of as many as possible incidental learning strategies to learn your target language and you will be a bit closer to your goal of learning a language.