A few weeks ago, at the Brunch & Language Exchange, the typical cliché came out when someone said that in Barcelona only Catalan is spoken…
That reminded me of an American guy who crossed the ocean for love and moved to a town in Lleida. Everyone there spoke only Catalan, so that was the language he learned. But after a few years, he and his girlfriend broke up, so he decided to move to Barcelona, thinking that a big city always offers more opportunities. His surprise was when, he arrived in Barcelona, he found that almost no one spoke Catalan; therefore, without speaking Spanish, his options for finding a job were limited.
When someone brings up this cliché, I usually ask: Where? In what part of Barcelona is Catalan the only spoken language?
Then, it usually turns out that it is not in the city, but in a town in Catalonia. Such thing has an explanation as simple as that if in towns people do not usually speak Spanish, it is because they do not need it for their everyday life. That does not mean that they do not understand it, simply that they do not practice it daily, therefore they are not fluent and do not feel comfortable speaking it.
I compare it to English. It is a language that we have studied for years in elementary school, high school, etc. But, generally, it is not a language that we use daily, all the films are dubbed into Spanish and we are not in the habit of using it at all. Then, when a foreigner asks us something on the street, we become paralyzed, we begin to sweat trying to remember what that teacher repeated to us for years and we feel as uncomfortable as those people who live in towns where Spanish is not used.
In short, languages must be practiced regularly to be able to use them without even having to think, it does not matter if it is a language very similar to yours or completely different, the more you practice it, the more fluent you will be and the more comfortable you will feel speaking it.