Shooting wide open isn't the sharpest aperture. Yes, it may be sharp where you want it, but if you want something so sharp it'll cut you then if your lenses' max aperture is 2.8 then it should be normally F/4 and if you have a 1.2 to a 1.8 then F/2 for 1.2 and 1.4 and I think F/2.8 for the 1.8. And for people with variable f/3.5-6.3 I find my lens to be sharpest at F/9 on down.
Now remember that's for the sharpest picture not the brightest. For the brightest you gotta know the exposure forumla. Which is ISO + shutter speed + aperture = exposure
Although you should think of it more as a triangle since if you increase the ISO and nothing else when you already had a correctly exposed photo, what you will get is a brighter photo. So be aware of the changes you make to your settings so you get what you were looking for.
Now to bring in the beginning statements I made together. Yes we all love that milky and creamy background that 1.2 and 1.4 gives us, but you gotta know whens not the time for that. Which would be moving subjects, you can try but more than likely there will be reshoots and compromises if you're not too careful. So, to avoid this just set the aperture lower so it'll be more sharper and just change your settings accordingly to have the exposure you want.