In fact, most people are inclined to believe that no one is irreplaceable. In fact - this is true and it is a good reason.
The first reason - genius.
Very often people say to be essential when it comes to man-geniuses or highly qualified specialists with extensive experience. In fact, such a person can be replaced. However, it is possible that it will have to look for not one, but several people. One of the command, for example, will have analytical ability is aware of the other in a desired region, and the third is an experienced technician.
The second reason - to stop.
Let's imagine that you need to replace the item in the car at the time when it is in motion. Agree to do so without damaging the components and mechanisms cars is almost impossible. Also now. Sometimes, in order to replace the very valuable employee, you must stop production. Moreover, a replacement will be successful only in that case.
Reason Three - a severe case.
In practice, the most difficult to replace the man who himself specializes in replacements. So, for example, a specialist personnel officer with a really high level of knowledge and capability, it will be difficult to find. However, this task can not be called impossible.
Reason Four - not all at once.
Note that when you replace a specialist who performs a simple but repetitive work, such as speed of execution of tasks from a new employee you can not be achieved immediately. Thus, in this work is very important experience - consider this.