The lens will have sharper focus if you close the aperture down a couple of stops.
DOF can get so sgallow that you leaning a little closer or farther from the subject can move the focus point in front of or behind the eyes. A tripod or a camera stand really helps too.
The point is that fast prime lenses don't usually get used by advanced photographers at their widest aperture. They get used at the widest aperture that still gives sharp focus and with a f/1.4 lens that will usually be in the f/2.8 - f/5.6 range (2 stops smaller aperture - 4 stops smaller aperture than f/1.4).