The trick was to connect the ball to the rest of the mouse at the two points where there was the least friction right where his fingertips had been, dead center on either side of the ball.

NEWYORKER: Creation Myth

Even in matters of pure physical reality, we depended on a friction between our basic faculties of sensation, his and mine, and we understood now that the rest of the afternoon would be spent in the marking of differences.

NEWYORKER: Midnight in Dostoevsky

But if it is simply bolted on to add transactional friction to prevent churn (through recurring billing), it will be hard to lined up the rest of the business model to address the other issues previously mentioned.

FORBES: New Rules For E-Commerce