One of the hardest and saddest things I ever had to do was convince my Dad it was time to hang up his keys. It would have killed him if he had ever hurt/injured someone.
Hardest day of my life was having to tell my grandmother that it was unsafe for her to be behind the wheel of the car. She nearly collided with a 3/4 ton pickup truck on the open road, and ran into two people in town. Was reported by three individuals. Highway Patrolman came out and helped me explain to her what might've happend.
She simply refused. The patrolman ended up taking away her drivers license, and I've had to hide her keys.