There are many factors that affect steady handholding.
Time of the day for example, how tired you are.
How many cups of coffee you drank.
How strong you are. How tall you are.
Your technique. Though if you have been shooting for awhile you should have developed that already.
Weight of the camera. Camera grip adds steadiness.
Shutter button. How much force does it take to push it.
Mirror slap.
Idiosyncrasies of the lens you are using. I have seen many articles where certain FLs and shutter speeds produce less desirable results.
Weight and balance of the lens. The hood of the lens and wind conditions.
Etc..Etc...