Varifocal contacts don't work in the same way as varifocal lenses.
With varifocal lenses, you simply need to train your eyes to look through the correct part of the lens to obtain the best focus.
With varifocal contacts, you can't move your eyes in relation to the lenses, so you are permanently looking through all of the lens - ie the parts that produce the correct focus and the parts that don't.
Instaed you have to train your brain to ignore the out of focus images and only interpret the in-focus part.
Some people have no problem with this, but in others it can induce headaches and poor results.
I, for one, failed entirely to adapt to varifocal contacts.