It was long claimed that each tether is backed at 1$. And historically we had very similar situation with gold certificates where we already know how it did end.

Gold Certificates

Gold was rather unpractical to carry around and divide up and validate. Instead to make trade more convenient many private banks offered gold certificates that were redeemable in gold at the bank and had a written face value. This value was backed by the gold reserves securely stored in the vaults of the banks.

Obviously there is a huge incentive for these banks to issue gold certificates without actual gold backing. And as long as the bank has about 10% of the gold, customers will never discover since they experience that they can liquidate their gold certificates. However when all customers redeem at the same time the system crashes.

The reasons why the banks started to issue fake gold certificates are very different. Some did out of pure greed, others because they messed up somewhere else and were in need of money. But over time almost every gold certificate was only baked by a fractional reserve. And as soon as this became well known it triggered a bank run. The people redeeming their certificates early left with their gold. The people that came later in a panic had nothing left but worthless paper.

USD Tether/ USDCoin / ....

A lot of the stable-coins are just a reinvention of this old system. Instead of having actual dollars, you get a dollar-certificate that promises to pay you dollars on request from a hidden stash of dollars. And because this stash cannot be verified, it has exactly the same problems as gold certificates.

If history repeats, we should expect to have crypto bank runs and these coins eventually crashing down to a value of zero. And for tether there are already clear signs that this may happen rather soon.

Initially tether had the reserves, but then bitfinex messed up and had trouble to access 750 million dollar. The story about this is not really settled and it is not clear what exactly happened.
But what we know it that tether then gave a 750 million dollar loan from their tether reserves to bitfinex. And while they now hold a loan of 750 million dollar, this loan does not have the same value as actual 750 million dollar (there is a 6% interest on that loan, but that interest will almost certainly not be distributed to the holders of tether that will however pay for a potential default.). Tether is therefore no longer fully backed and this is not a conspiracy but a proven fact. And 750 million dollar is about a fourth of their total reserves.

And this will not only continue to happen for tether but for all centralised stablecoins. Right now tether is still valued at 1$. I would suggest it is time to get out so you do not end up being the last person in the eventually coming crypto bank run.
I am not a big fan of MAKER/DAI, but if you choice is tether or DAI, then I know what I would choose.
Because in crypto there is no need to trust in hidden dollar reserves. We can build public verifiable stablecoins that do not require trust and that do not have the same flaws of fractional reserve systems.