It is what we mean when we claim someone is "incapable of <x>" such as murder. It does not mean they do not physically possess the means, but rather that they lack the psychological impetus to do so.
More relevantly, a person who is both capable and willing to restrict your freedoms, potentially even unto death, has more control over you than a person who doesn't.
This isn't abstract theory. This is a description of "government". Would you pay any attention to the people claiming to be "the government" if they didn't have credible mechanisms for backing up their demands?
It is preferable that government not be solely founded on this power relation. It shouldn't be considered "sufficient" for good government. But it is certainly "necessary".
https://en.wikipedia.org/wiki/Monopoly_on_violence
It's why "non-coercive government" is an oxymoron.
Say you can kill a man, but irregardless of the threat to their life said man would refuse any and all of your orders, who can then be said to have 'control'?
In the end control means the ability to influence outcomes. There are many metrics, and for some choice of metric the capability of destruction is control.