The basis.

Council Manager Form of Government.

The Manager
A city manager is appointed by the city council. In theory, the council makes policy and the manager sees that those policies are carried out. However, the manager and city bureaucrats may have been responsible for suggesting the policy in the first place, thus the city manager often does make policy and sets general directions behind the scenes through his or her influence over the council.

The Mayor
The mayor’s job is largely ceremonial. She presides over the council, and represents the city in various ways, but has no real power except as a member of the council.

Advantages
The central advantage of having a city manager is that he gives full time professional management to city business. In most cities, the council and the mayor are really part time amateurs.

Power
Certainly the office of mayor is an ideal platform for proclaiming need for change. However, mayors who come to office with high hopes of accomplishing great things soon collide with a few unexpected realities of public life. They may be surprised by their lack of real power. They learn how many things are not up to them to decide, and how many boards they must go through to make changes. They find that bureaucrats often arm themselves with political support, in excess of the mayors own.  Mayors discover that things they want to accomplish means changing things, but change means colliding with every interest satisfied with the status quo.

Influence
Why are city councils so docile in the face of city managers and agency heads? Councils routinely enact the policy recommendations of administrators, generally without much deliberation and without inserting many changes. Because many of these things are detailed, complex and require specialized knowledge to simply understand what is going on. A city council cannot possibly know as much as the experts and bureaucrats working on these projects. They must rely on the experts to supply the information to them. Otherwise they will bumble into stupid decisions that may prove very costly.

Another reason is that city council members are often poorly paid. Most time that they can afford to spend on city business is often taken up with routine. Most city councils meet once a week, and by the time they have dealt with the mundane and miscellany the meeting is nearly over. Little time is left for pondering the obscurities of large issues.

(An overview of parts of chapter 10, State & Local Politics, Robert S. Lorch.)