Why do virtually all successful candidates hire a campaign manager?

A campaign manager is essential to a political campaign because they help to assess data, analyze patters, and organize the events that the candidate must attend.

For example, a campaign manager may see that a presidential candidate really needs to win a certain state in order to become president. The campaign manager will then organize several events in that state, targeting the demographic they need in order to win the election. Along with this, having a campaign manager gives the candidate themselves more time to interact with citizens and to worry about other aspects of the campaign.