The initial reasons for the decline of UST to 0.98 USD and below were a sell-off in the cryptocurrency market and the actions of an unknown seller, who sold $300 million worth of Stablecoin on May 8. This was accompanied, probably on purpose, by provoked discussion of UST weakness in social networks, which led to panic and significant pressure from other market participants. For a while, market makers tried to restrain the UST exchange rate by selling Bitcoin and other crypto-assets, but it did not save the situation.
