I'll share one, an expat friend of mine from Russia would always take all his euro earnings and immediately convert them to rubles because the interest rate was quite good back then (2012).

I would constantly badger him about this because I was like, 'this is madness, a Russian with half a brain cell would never keep all their savings in rubles, and here you are'.

his excuse was always that he wanted to buy a flat and would need a large sum in rubles ready, even though doing a simple international bank transfer was not a big deal back then.

anyway, sure enough, after the annexation of crimea and sanctions + the oil price dropping, he ended up getting smashed. He did manage to get a flat in one of the poorer Russian regions eventually, but he lost probably the equivalent of 20-30k+ euros in the process.

if he had just kept it in Euros and done the transfer when needed, he would have come up like a boss.