He'll hurt himself unless he's very careful.

If he isn't very careful, he'll hurt himself.

He won't be able to go to the party unless he can find a ride.

 She'll continue to have problems with her teeth unless she gives up drinking sugary soft drinks and eating candy.

Unless the restaurant can improve its business, it will have to close.

 Water from the kitchen faucet can be as good as bottled water unless it really tastes bad.