The first couple of years in a position of power at a company can be quite uncomfortable.
Whether it is giving end-of-year reviews or having to write somebody up, there will be new situations that you will have to deal with regularly.
A manager that is uncomfortable to act or reprimand employees in uncomfortable or stressful situations can quickly lose the respect of those working for them.
Setting a tone of competence is important from day one as a new manager trying to find their voice can quickly be trampled.