An automatic transmission makes driving wonderfully uncomplicated. Put the car in Drive, press the accelerator, and let the machinery handle the complicated stuff. Unfortunately, some drivers treat that convenience as permission to do whatever feels easiest behind the wheel.
A quick shift into Reverse before the car stops completely, a little accelerator pressure to hold position on a hill, or skipping the parking brake might seem harmless. Your transmission may have other opinions. And considering what transmission repairs can cost, those opinions deserve respect.