DAI, like other stablecoins, isn't really all that stable - right now it costs about $1.02 to buy $1 worth. And, it's frequently been over 5% away from $1: https://coinmarketcap.com/currencies/dai/#charts

Most "stable" coins are trading at over $1 right now, presumably as people try to flee sinking cryptocurrencies and have no practical and/or legal means to turn them into real money.

It doesn't have to always be exactly $1. You obviously can't control markets and what people sell things for...but DAI has mechanisms in it's protocol so that the price trends to $1. It's incredibly fascinating, it's decentralized, permissionless, loans with an economic system backing it. It's very novel tech and a huge achievement.