Here's how it works: Drivers do not open their door with their left hand, which is closest to the handle, but with their right hand. Not only can they look in the left wing mirror before opening the door, but they will almost inevitably also look over their left shoulder - and may therefore recognize a cyclist or pedelec rider approaching from behind in the "blind spot".
The driver in our symbolic image does it wrong: she uses her left hand to open the door and doesn't notice the cyclist approaching from behind.
Passengers sitting on the passenger side naturally use their left hand to open the door.
The trick is called the "Dutch grip" because - you guessed it - it probably originated in our neighboring country. Many people in this country also learned it this way at driving school.
Your Recklinghausen police wish you: Always reach your destination accident-free!