Immigration involves long lines and probing questions (and back in the Ellis Island days, possibly actual probes). And that's just if you leave politics out of it. Just like leaving one country behind for another, application migration is not easy. Application migration occurs when an application is moved from one environment to another. In current context, most application migration is from on-premises servers to the cloud or between clouds.
Application migration can be tough because of the differences in hosting platforms. Similarly, people who are raised in one country will have a learning curve in a new country no matter how much they prepare ahead of time. Even moving between countries that speak the same language can be difficult (think of the differences between the United States and Australia). As such, cloud-to-cloud migrations might be easier than on-premises to cloud, but even cloud vendors have unique ways of operating that make cloud-to-cloud application migration challenging.