Blame the Swedes is the latest theory.
A few years ago, the Swedish bank Nordea set up a wind machine near the centre of Riga, within sight of the Freedom Monument, and created a small whirlwind of Latvian board game banknotes.
The 'cash' swirled around in a funnel several meters high in front of stunned and fascinated pedestrians. The message was not to miss out on the whirlwind of cash Nordea was offering the Latvian public.
They got the message. They just couldn't pay it back.