Imagine the grip as two sumo wrestlers. They are balanced in the canoe, but there are many ways to be balanced in a canoe. If the two guys are sitting centered in the canoe they can row down the lake in a straight line with speed. Either one or both can stand up and the canoe stays balanced in the water. If they are balanced in the water but one is on the left side of the canoe and the other is on the right, they can row down the lake but very carefully. As soon as one of the guys stands up the canoe tips over.
The golf grip is the same. We need to keep both hands on the club in balance relative to the forces of nature, because if one hand decides to “stand up” (grip pressure change, etc.) the clubface tips over. Check your grip one hand at a time. They both should be on the club so that the face remains square during your swing.