What makes the managerial task of executing strategy so challenging and demanding is the

Trial$-$and$-$error experimentation that is required to come up with a workable organizational structure.

People$-$management skills required, the resistance to change that has to be overcome, and the perseverance necessary to get initiatives involving different functional areas of the organization launched and kept moving along.

Time and effort it takes to build core competencies.

Supervisory requirements associated with getting company personnel to do things the right way.