To be inert means to have no power or strength of action or motion. In chemistry, it is used to refer to any gas that has little or no ability to react. In reality, there are some people who can be inert towards things concerning them and sometimes others. In this case, they are sluggish to act even when it is something that will benefit them.
There are people who may be slow to act, react, lack the strength to move due to some physical ailment. For instance, it is quite understandable for a patient lying critically ill in the hospital to be motionless due to lack of strength. Again, there are other sets of people who may be inert due to emotional stress.
It is not wise to wait for others to push you before you stand up and act on issues concerning your welfare and life in general. A lot of times it will cost you when you live your life in that manner.