The trigger is not a light switch, it is a mechanical lever. This mechanical lever is not rigidly affixed to the handgun.

Make a completely safe weapon and pinch the width of the trigger with your thumb and forefinger.

You will notice the trigger can be moved side-to-side. Why does that matter to the marksman? If the trigger is not deliberately brought to the rear in straight rearward movement, the shooter will negatively influence sight alignment during trigger press.  Dry fire is the easy cure for a wandering trigger press.

Lesson: Gently pressing the trigger is not enough for good marksmanship.