Functions of management

Controlling is one of the four functions of management equally important as planning, organizing, and influencing even though our book really devotes little time and attention to it. Most management books do the same thing. I don’t get it personally because I think it is such an important function and without it whatever managers do in planning, organizing, and influencing doesn’t get measured and will never reach the highest level of effectiveness and efficiency.
Explain, in your own words, why controlling is such an important component of the management process? What can you do as a manager to ensure that the control function is successful?