avoir la tête sur les épaules

to have good, sound judgement

Used to praise someone who keeps a cool, practical head about them, especially when others might panic or lose perspective.

Malgré la pression, elle garde la tête sur les épaules et prend les bonnes décisions.

Despite the pressure, she keeps a level head and makes the right calls.

The image is simple: a head sitting squarely and steadily on the shoulders mirrors a steady mind, since the head has long stood for reason. It's often set against perdre la tête, to lose one's head.