observeOn vs. subscribeOn

Cross-thread subscriptions is a question that seems to pop up again and again on the RxSwift Slack channel. The explanation is very simple so I thought it was a good idea to put it in a blog post so whenever needed I can link to it instead of typing everything again and again. Observable subscriptions The terminology in regard to subscribing and observing is imho a bit messy so let’s first take this out of the way (do not skip this section!