For me, the surprising part was learning how many Russian people I know have parents or grandparents who were born in Ukraine.
I knew that Soviet Ukraine had ~50 million people. Almost 20% of the USSR, and a bit less than France, Italy, or the UK at the time. I knew that Ukraine was one of the most developed and densely populated parts of the USSR, and of the Russian Empire before that. I had some idea how the borders had moved over time, and how the cultural boundaries were ambiguous as a consequence. I just had not realized how often that ambiguity would show at individual level.
I knew that Soviet Ukraine had ~50 million people. Almost 20% of the USSR, and a bit less than France, Italy, or the UK at the time. I knew that Ukraine was one of the most developed and densely populated parts of the USSR, and of the Russian Empire before that. I had some idea how the borders had moved over time, and how the cultural boundaries were ambiguous as a consequence. I just had not realized how often that ambiguity would show at individual level.