Does "not a scintilla more (or less)" mean "not a bit more or less"?

Plus, does " in this department" mena "in this part of the world"?

Context:

You are not in control of your mind - because you, as a conscious agent, are
only part of your mind, living at the mercy of other parts. You can do what you decide to do - but you cannot decide what you will decide to do. Of course, you can create a framework in which certain decisions are more likely than others - you can, for instance, purge your house of all sweets, making it very unlikely that you will eat dessert later in the evening - but you cannot know why you were able to submit to such a framework today when you weren't yesterday.

So it's not that willpower isn't important or that it is destined to be underminded by biology. Willpower is itself a biological phenomenon. You can change your life, and yourself, through effort and discipline - but you have whatever capacity for effort and discipline you have in this moment, and not a scintilla more (or less). You are either lucky in this department or you aren't - and you cannot make your own luck.