back on the rails

What is the origin of the idiom "back on the rails" and when to use it?

The phrase 'back on the rails' comes from the world of trains and railways. The 'rails' in the phrase refer to the parallel metal tracks upon which train wheels run. To keep a train moving in a straight line and prevent it from going off the tracks, it must stay 'on the rails.' If a train does go off the track, it must be put back "on the rails" before it can continue on its journey. Over time, the phrase 'back on the rails' came to be used metaphorically to describe the process of getting back on track after a setback or problem. It implies that, like a train, a person or project may temporarily have gone off the tracks but can be put back on course.