I hear people say this all the time, but I don't think it's true AT ALL!
I learned Portuguese without ever visiting a Portuguese speaking country, and I know many people who achieve good fluency and accuracy without visiting the/a country where the language they are learning is spoken.
I do some basic training for the most used verbs and vocabulary on my own...then I find a tutor and I do language exchanges, listen to podcasts, read books and articles.
What do you do to immerse yourself in the language? Do you believe it's best to learn the language in the country where it is spoken?