Having ruined your day, I'll now tell you how to consistently achieve acceptable sharpness for your purposes.
The key of course lies in "acceptable" and "your purposes". There are many things we can define and measure very accurately - distance, weight, horsepower, etc. - unfortunately sharpness is not one of them. I have spent much of my life plus sums of money I don't dare disclose to my wife trying to achieve ultimate photographic sharpness.
There is much which affects sharpness - some you can't control, but some you can.
CAMERA SHAKE is one of the most common causes of unsharp photos. Ideally one should always use a tripod, however circumstances often preclude using one. If you do opt for a tripod, please invest in a good one; "cheapies" are often flimsy and have inherent vibration rendering them worse-then-useless.
If a tripod's out, consider using a monopod, which is basically like one leg of a tripod with a camera-attachment at the top. Whilst you still have to "hand hold" a camera mounted on a monopod, you'll be amazed how much steadier it is whilst maintaining good freedom of movement. If you doubt the worth of a monopod, check the pro photographers at a sporting event. Those $10K - $15K camera-lens combos are often aided by a $150 monopod.
If your photography allows a camera to be fixed in a permanent or semi-permanent position (photographing your stamp collection, for example) a copy stand or camera bracket may be an excellent solution.
If none of the above is possible, at least try to brace your arm(s) against something solid as you take a photo. Think you can hand-hold a camera successfully? Well, your hands may be sufficiently steady for neuro-surgery, but your heart-beat is enough to take the edge off sharpness.... even at higher shutter speeds!
If you feel I'm being picky in the above statement, you're right, however image degradation is cumulative in many instances, so everything you do to minimise degradation ultimately enhances sharpness. On to Page 2, please.