Why do I get "CS0120: An object reference is required to access non-static member..."

I have the following code:

        ....
        StartCoroutine (DealTheCards ());
    }

    IEnumerator DealTheCards() {

        int theLoop = 52; 

        while (theLoop > 0) {
           
            yield return new WaitForSeconds (rateToDealSeconds);

            print ("theLoop: " + theLoop);
            theLoop--;

        }

    }

I get:

CS0120: An object reference is required to access non-static member `UnityEngine.MonoBehaviour.StartCoroutine(System.Collections.IEnumerator)'

Could someone nice explain to me what the problem is?

Whatever it is that is trying to StartCoroutine is static, and that’s impossible (apparently)