The set-up: Tether was, to a layman, a decent idea. The build-up: As creation and redemption was demonstrated, Tether attracted buyers. The snag: Tether got hacked [1] and released an IOU to affected customers [2]. Wells Fargo got spooked and froze Tether/Bitfinex [3].
The fudge: Tether has a hole to plug. They also have nowhere to put incoming U.S. dollars. Someone suggests they buy Bitcoin with the incoming dollars. The stupid figure it's a temporary measure until they find a new correspondent bank, the evil smell a scam and the lazy don't think about it. Bitcoin ascends. This move becomes very profitable. (It also increases the size of their balance sheet, which makes finding a new correspondent bank more difficult.)
Doubling down: Bitcoin descends. The firm becomes, or comes close to becoming, insolvent. Tethers are issued to bring the balance sheet back into line. The stupid figure they can unwind when Bitcoin recovers; the evil and lazy agree to not think about it. The frequency and magnitude of this "support" keeps growing.
The collapse: At each development, the smart and ethical decamp. That leaves everyone on board too incompetent, distracted or lazy to properly address a journalist's investigation [4]. That, in turn, attracts regulatory attention [5].
[1] https://www.theverge.com/2017/11/21/16684296/tether-cryptocu...
[2] https://www.coindesk.com/bitfinex-disperses-unique-token-to-...
[3] https://www.coindesk.com/bitcoin-exchange-bitfinex-sues-well...
[4] https://www.bloomberg.com/news/articles/2017-12-05/mystery-s...
[5] https://www.bloomberg.com/news/articles/2018-01-30/crypto-ex...