Misleading statement by Lew Lorton too. Chris statement is quite correct when you talk about “refraction” while Lew is talking about faster shutter speed to minimise motion blur, camera shake etc. Both are quite correct depending on what causes the “blur”

When discussing the lens opening - or f stop - the larger the number the smaller the opening. Thus f 16 is a smaller opening than f 2.8.
The larger the opening the faster light can get into the camera.
The smaller the opening, the slower light can get in but the greater the depth of field (the distance in front and behind the actual point you are focussed on that seems to be in focus.)

If the light stays constant, making the aperture smaller (increasing the number) means that one must decrease the shutter speed (lengthen the amount of time the shutter is open). Think of any exposure as a container. To fill the container you can pour a great deal of water for a short period of time (large opening, fast shutter speed) or you can pour a little water for a long period of time (small opening, fast shutter speed.)

So, if you are taking portraits and want only the face to be in focus, an f stop like 2.8 might be in order; thus the face would be in focus and the background out of focus. For a landscape, you might be using f16 so that much of what you see from close in front of you to the horizon will be in focus.

Usually the lens is sharpest at an f stop that is 3 or 4 stops from its maximum aperture. I.E. a lens with an maximum opening of f 2.8 might be sharpest at f5.6 or f 8.