Sarah has been working for a small sheet metal shop for a few weeks. Tom and Bill are the two foremen that supervise activities in the shop. Both Tom and Bill give Sarah orders from time to time, and the two sometimes give her conflicting instructions about what she should do$.$ Sarah doesn't want to make either Tom or Bill mad, but she is confused and frustrated by these conflicting assignments. This type of situation represents a violation of Fayol's $\_\_\_\_\_\_\_\_\_\_\_\_$ principle.