Let’s say that your “nervous space” is limited to 3 nervous actions. This means that at any moment you can run at most 3 nervous actions without losing control over them.
Suppose that there are nervous actions A, B and C.
Suppose that your “nervous space” is empty at this point. Suppose also that it receives no input from any source other than your own will. This means that your “nervous space” will remain empty until you fill it with some nervous action using your own will.
Now, suppose you decide to put nervous action A in it. The state of your “nervous space” will now change from being empty to containing nervous action A. Let symbol “A” be a representation of such a state. The state of your “nervous space” will remain as such, which means “A”, until the next time you decide to change it, say by removing the nervous action A from it or by adding another nervous action to it.
That a state of an object remains to be what you have configured it to be until the next time you decide to reconfigure it is what it means “to have control over the object”.
In our case, this object is “nervous space”. Therefore, our control is control over our “nervous space” which is what is meant by the phrase “to have control over ourselves”.
We can now change the state of our “nervous space” to “AB”, indicating that it contains nervous actions A and B, or “ABC”, indicating that it contains all three nervous actions. In both cases, we will remain in control of our “nervous space”, because in both cases, the maximum number of nervous actions our “nervous space” can contain is not exceeded.
To be in control, remember, means that the state remains the way we have configured it. This means that it remains “ABC” if we have configured it to be “ABC”.
Now, suppose there is another nervous action “D” that we want to add on top of A, B and C such that the new state is “ABCD”.
But this is an attempt to insert 4 elements within a space that can only contain 3 elements.
So what happens then?
The same thing that happens to a cup full of water when you try to add more water: it overflows.
By forcing nervous action D within your “nervous space” that is at full capacity, you can make sure that nervous action D finds its place within it, but the rest will have to accommodate to that by removing one nervous action.
Which one, you may ask. Any one. The action to be removed is determined randomly.
So instead of “ABCD” you will get some combination of “xyD”. Either “ABD”, "ACD"or “BCD”.
Instead of what you want (e.g. “ABCD”) you will get an imitation of what you want (e.g. “ABD”.)
This is what it means to lose control over yourself. Instead of deciding what’s going out and what’s staying in, you are simply throwing a dice.
In our example, the capacity of our “nervous space” is 3 nervous actions, but in reality, the number is far greater than that.
Where numbers are larger, there loss of control is worse.