To live hand to mouth is to have only just enough to survive on. They live hand to mouth.
Nothing is left over, so any small emergency becomes a crisis. The picture is of food going straight from the hand to the mouth with nothing put by.
1phraselive hand to mouthTo have only just enough to survive on.
“The family had to live hand to mouth for the whole of that winter.”
live hand to mouth is a phrase.
Practised in Idioms