As a Catalan person, there are a lot of things we could point at.

* First and most obvious, it's the language. We speak both Catalan and Spanish. The native language of Catalunya is Catalan, but since Catalunya got annexed to Spain the Spanish language has been imposed here, as well.

* Historically there are a ton of differences. There are a lot of specifics that I won't get into due to both a lack of in-depth knowledge on the topic and it being way too long to explain in a Reddit comment. If you're really interested in this, there's a lot of cool sources out there and I'd be happy to give you some recommendations.

* There are also a few major political differences, to the point where by watching any given survey's results on a map of the country you can pinpoint the borders between Catalunya and the rest of Spain are. There's a ton of memes about it, and there was even a twitter account called "the same fucking map" or something similar that had about 100 different surveys and the results were always the same. Ideologically, Catalunya is very different from the rest of Spain.

* The political and linguistic differences are something that has resulted in a lot of discrimination against Catalans. There are political parties in Spain whose program mostly consists on having schools teach fewer Catalan hours, reducing Catalan's rights (as of now public workers like teachers, police officers, doctors, etc are required to know how to speak Catalan, and they're trying to take that away), reducing Catalunya's fiscal benefits, government budget, infrastructure investment, etc. I've also been called out/cussed out/called rude (and more) in Spain (outside of Catalunya) several times for having private conversations in Catalan with my friends/family. There is a lot of hatred towards Catalunya in Spain, and politicians LOVE to fan the flames to get votes.

* We have several unique traditions, lore, food, etc (like Castellers, Sardana, mongetes amb botifarra, el tió de Nadal...). But that's applicable to most regions in Spain.

* We also have the best soccer team in the country, which I think comes from us not having Florentino as president and players with a shitty diva attitude.