I wrote a long comment but it was too long, so I'm going to try to split it up into separate comments:

Part 1:

I moved from Miami to Kyiv, Ukraine three and a half years ago. I see a lot of interesting responses from Western Europe, but OP didn't specify where in Europe so I'll give my EE perspective.

I live in the city center in Kyiv, which is a great city, vastly underrated due to the legacy of the Soviet stereotype.

Big sacrifices, in no particular order:

- Others have mentioned that the houses are smaller in Europe; this is true here as well. But it's not just about the space; apartments here (and the houses I've been in as well) as just not a comfortable. The stairs are steeper, the layout is weird (especially in old apartments like mine which dates from the Stalin era), the corridors are dirty and dark, if there's a clothes washer at all it's in the bathroom and there is no separate dryer. I admit non of this really counts as a "big" sacrifice, but it's something I still notice every day, even after years of being here.

- As I mentioned, I came here to build a company, so I'm not earning a salary on the local economy. The US is by far the best place to earn money in tech, others have already reported that. Ukraine salaries are cheaper than Berlin, but for strong and in-demand talent, not a whole lot cheaper. The absolute top of the market at this time of crazy salary growth is probably USD 7K or 8K/mo; a more realistic salary would be USD 4K to USD 6K/mo. Compared to the US that's shit, but the Ukrainian tax code has a special carve-out for IT, so the income tax on that is only 5%, and the cost of living is pretty low. I think as a foreigner if you could find an IT company that would hire you for a reasonable salary you could set up quite a comfortable life for yourself, although as I said I haven't personally done this.

- I took for granted that in America, foreigners can immigrate and become Americans, not just by law as citizens but in the eyes of other Americans. That emphatically does not happen here. I could live here for 40 years, earn Ukrainian citizenship by serving in the Army, raise Ukrainian children, and when I die, I will die a foreigner. Most Ukrainians I meet are not hostile to foreigners, but they also don't treat me as one of them, and many assume all foreigners are rich and will try to cheat you. I've grown used to this, and it doesn't bother me, but make sure you're prepared for this reality.

- This sounds stupid, but Amazon (and the ability to impulse buy things and get them the next day, in general). The local market has a lot of Western products, but the markup is insane. Ukraine has very unreasonable import taxes on foreign goods, so everything here is much more expensive. Cars could easily end up being 2x the cost of the equivalent in the US. Residents are allowed to import packages worth up to EUR 100 without import duty; after that, it's 20% tax. Amazon does ship some things to Ukraine, but the shipping is unreasonable and almost everything they still will ship to US only, so I use a service (Meest) that provides me with an address in Delaware, and then will re-ship my packages by boat (takes over a month) or by air (takes at least a week and costs a lot more), where I can receive them at the Ukrainian equivalent of FedEx. Obviously this elaborate process and restriction on dollar amount means I rarely order things from abroad. This might be the most first world of problems ever complained about, but I really do miss this.

- Practically no one you will encounter in daily life, outside of tech workers, will speak any English. This was very hard for me because I'm very self-conscious about making mistakes speaking a foreign language. I speak Russian now at an intermediate level (I really should learn Ukrainian, but Russian learning materials are so much more abundant, and I can use Russian in other countries in the region), which has helped immensely. I can't emphasize enough the importance of speaking the local language with at least conversational fluency. It used to be I wouldn't order food delivery because I know they will call me to confirm the order (this is an annoying cultural difference BTW) and I'll struggle to understand them and it'll be a mess and it's better to just eat some crackers. Now I have no fear of communicating, not because my Russian is perfect, but because I've been here long enough and studied enough that I know I'll be able to communicate. If I had not invested multiple hours per day early on in language study, I doubt I'd still be here. It's just too hard, and too isolating.

- The healthcare system here is...not up to Western standards. In summer 2020 had a heart issue, and was really unsure if I needed to evac back to the US or not. I felt like I would die, although my cardiologist in Ukraine said that was very unlikely. Dealing with the healthcare system is really not pleasant for me, thankfully my girlfriend helped with some details. The process is utterly foreign, and bedside manner is not emphasized in Ukrainian medical schools. So if you come here, don't get sick, and if you do get sick...make sure a Ukrainian cares enough about you to help.

- I left all of my friends and family behind. There's no getting around it, that sucks and there's no solution. Ask yourself how badly you want to move. I don't regret my decision but I won't pretend it was easy. I doubted myself many times. It's not easy for me to make new friends even in my home country; it's no easier here. I am friends with the guys I have hired on my team, but I wouldn't say I have any close friends here.