NECESSITY is a force propelled by a specific circumstance.
Dictionary dot com has one definition that would fit in this story by one Happy Guy:
(5) an unavoidable need or compulsion to do something: not by choice but by necessity.

A couple fly-campers were running low on food in northern BC a week before the helicopter was scheduled to pick them up. Worry turned to desperation when a bear broke into their food cache and stole most of the food.
What to do?
They hunted down the bear and indirectly recovered their stolen food in the form of boiled bear meat. Not the tastiest, but it sure beats eating tree bark.
There are always opportunities cleverly disguised as obstacles. Hunt them down.
And hunt they did!