そうしないと

expression

otherwise; if not; or else

Used at the beginning of a sentence or clause to state what will happen if the preceding action is not taken. Often implies a negative consequence.

• 早はやく起おきなさい。そうしないと遅ち刻こくしますよ。

  Get up early. Otherwise you'll be late.

• 傘かさを持もって行いったほうがいい。そうしないと濡ぬれるよ。

  You'd better take an umbrella. If not, you'll get wet.