cannot avoid or help doing something
必须，不得不
they must needs depart.
他们不得不离开。
it is or was necessary or unavoidable
必须，不得不
if needs must, they will eat any food.
如果必须的话，他们什么食物都要吃。
(proverb)sometimes you have to do something you would rather not
(谚)情势所迫，只得如此