Firstly, shooting at f1.4 means super accurate focusing because zone of sharpness may only be a few cm, depending the camera to subject distance. This means that the slightest shift will result in a blur picture. And most lenses are never the sharpest wide open.
Also it depends on the shutter speed - in the shade iso 200, shutter speed can be as low a 1/60 for f1.4 while out in the open is 1/2000. If your handholding technique is not good, the image will not be sharp even with stabilization.
Solution - practice. I shoot wide open most of the time, at shutter speeds as low as 1/30 no stabilization. The slightest shift will result in a less than sharp image, whether due to focusing, or wrong hand holding technique or both. I have been practising for 20 years and still no guarantee.