I heard it somewhere: we can live without food for a month, without water for a week, but we can't live without hope. Is this true? and if it is Why is it? What does it actually happen in our bodies?

Seems like once we reach the stage of hopelessness, we just give up and our brain just shuts down everything. I’m not considering suicidal thoughts. This proves our brain can either keep us alive or decide to shut down itself.