https://en.wikipedia.org/wiki/Catalan_independence
My take: Catalans are a National Minority in Spain. Catalonia has its own government, culture, language and, quite important, different political culture. Just to give you an idea, the party of Rajoy (Spanish president) that wins with majority in Spain election after election, got only 8% of the votes in the Catalan Parliament.
After the death of the Fascist Dictator General Franco, many catalans thought that Catalonia would be able to thrive as a Nation inside of Spain. This general opinion lasted for many years but, since 10 years ago, the attacks of the Government of Spain against the autonomy of Catalonia have made many people change their minds and realize that that the only way Catalonia will survive is by getting its own State.
> why tf would people want to "break" a country that works so well
Spain does not work so well. It has a massive unemployment and some of the lowest salaries in Europe. The economy is f* up and the Spanish government just spent all the money that was supposed to be used to pay our public pensions once we retire.
Also, the most important thing for me, is that most of the politicians in the Spanish main political party (PP) have direct links with the Fascist Dictatorship. Could you imagine a minister in Germany was the son of a Nazi official? Well, this is quite common in Spain.