From the Lucky Resistor blog:
Older people often have troubles opening plastic bottles. Also, people with gout or other disabilities lack the required strength to turn the small caps independently. The reason is the small diameter of the caps, which requires a strong grip with just two fingers.
There exist a variety of helper tools, assisting this task by increasing the leverage. A common problem with these tools is the static design. So if the manufacturer changes the size of the bottle cap, they do not grip properly anymore.
Recently, Lucky Resistor also made a beautiful design in our After Dark service.