It takes time getting used to the feel of the knife, and for the knife to break in a bit. It is a lockback, so resistance is present throughout the entire opening motion, making it more difficult to flick. I've not been one to be able to thumb flick lockbacks open, and prefer not to for the safety of my thumb. I almost always middle finger flick open Spydercos - it even works well on lockbacks once you're well practiced. Pinch the handle just in front of the lock between your pointer finger and thumb. Place your middle finger in the Spydie hold from the back of the knife, finger nail pointing the direction the blade will point when open. Quickly snap your middle finger up, in the direction the blade will be when open, and let it naturally curl away as it opens. I've found it to always be perfectly safe and quick to open them this way.