Calm allows priorities to remain recognizable.

Under stress everything starts to feel equally urgent, and the ordering of what matters disappears. That is when people spend their remaining energy on something minor while the important thing goes unattended. Staying calm is largely what keeps your sense of priority intact, and priority is most of what you need in a crisis.

When things are difficult, name the one thing that matters most, out loud or on paper. Then check what you are actually doing against it. The mismatch is often striking and easily corrected once seen.