If handguns are held too firmly, or not allowed to recoil "normally", bullet impact can be low. Underpowered ammo can also exhibit low bullet strikes. In addition to this, the vast majority of shooters tend to pull the muzzle downwards while firing, again with low bullet impacts being the result.
When the trigger is pulled, what we are trying to do is separate the sear from the hammer, which allows the hammer to fall. The same basic path is followed with striker fired guns. When the trigger is being pulled, we exert a lot of rearward pressure. At the moment the hammer or striker is released, the pressure from our trigger finger is still there. How this pressure is contained or dealt with affects accuracy.
As target shooters, we want a lightweight trigger pull, not because we are weaklings, but because the pressure exerted is easier to control. An overtravel stop or screw physically prevents the trigger from continuing it's movement, effectively containing the pressure. If the pressure is not contained, the sudden release of the sear allows the trigger finger to travel rearward at a higher speed, this is what we call "flinch", and the result is movement or wavering of the muzzle and inconsistent POI.
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For practice...
~ Only use the muscles in the trigger finger to pull the trigger.
~ Dry-fire with your eyes closed.