Unfortunately, it is not every time when you learn something new that your brain changes and grows. There are a few factors that need to be present for learning to effectively alter your brain. It doesn’t really matter whether you learn something out of need, curiosity or you are really thirsty for knowledge. Learning will only impact your brain physically, causing growth and plasticity, when the outcome of this learning will have behavioral consequences.
In other words, you know that your brain’s plasticity has changed if you apply the new knowledge.
Motivation and pleasure of learning are also important but in a different way. When you really enjoy the process, you will be more focused and therefore pay more attention, which will result in better knowledge retention and hence faster understanding of the information. You can then start using it faster and improve even further.
Motivation, on the other hand, determines how consistent you are when you learn a new subject. More motivation means more dedication and hence more time spend on the subject and more repetition, which again brings you to the point of faster knowledge acquisition.