Impulses

"I had desired it with an ardour that far exceeded moderation; but now that i had finished, the beauty of the dream vanished, and breathless horror and disgust filled my heart. Unable to endure the aspect of the being I had created, I rushed out of the room, and continued a long time traversing my bedchamber, unable to compose my mind to sleep." pg 35

The entire chapter before this point spent time building up the creation and the creation process. Victor Frankenstein has spent months, his first year of college, working on the animation of an inanimate project. Shelley makes a point to describe how consuming the process is and how much it taxes Victor. Not only does his social habits deteriorate, but his physical being begins to decay. His eyes are described as popping out of his skull. So months and months of labor and study and stealing bones to make the creation lead up to one dramatized moment. Thunder and lightning are crashing and Victor is marveling at the beauty of his creation. Until it opens it eyes. It's like a light switch goes off and Victor is suddenly terrified of his creation. Just like that, all his feelings toward it changed despite the months before that set up his master piece.

Again, later, Victor sees the creation for the second time and immediately thinks that it killed his brother, William; even though that theory is far fetched and unlikely. Victor is displaying a tendency to make up his mind suddenly and permanently and irrationally. His theories are fear-based very impulsive. This could lead to some interesting plot twists later on.