First and foremost, language. It's the basis for everything. Until you have the language learned, you are not going to function well. It doesn't matter if you were the highest-end professional in your original country; if you can't practice your profession in the new language, you have no profession. You cannot watch local TV, you have trouble with basic tasks such as buying groceries, reading signs and riding public transport. Language is problem number one.

Then there is the adaptation to the new governmental and bureaucratic structure. You basically need to figure out from scratch how a society works. For example, I moved from the 1990-s Russia to Israel. I had to figure out how healthcare worked. In Russia, everything was uniform and state-run and you were registered to a certain clinic by residence. Everything was free, officially at least. In Israel, there are several compering HMOs and I had to choose the best one for me by comparing prices and service - not an easy task when you don't yet know the language.

Then there's the sheer culture shock. People in different countries do not behave the same. The Israeli people, for example will often strike a new immigrant as rude because they are often loud, they do not have the same concept of personal space as Europeans. Someone keeping their distance and recoiling from an uninvited tap on the shoulder may be seen by them as cold and unfriendly.

One problem that blindsides every single immigrant and is rarely discussed is finding oneself a member of a minority culture. You come from a country where your holidays are state holidays, and suddenly they aren't, but it takes you years until you connect enough to local holidays to see them as yours. In Russia, for example, the New Year is a huge public holiday, but for a Russian immigrant in Israel the New Year is "that holiday that the Russians celebrate". It's a regular working day, which is a problem because Russians traditionally drink heavily on New Years. There are no grand shows on TV, no decorated fir trees in the streets, no New Years atmosphere as the Russians living in Russia know it. The "loss of holidays" is a bigger problem than it appears because it turns the year into one long monotonous routine that exhausts you more than you realize.