Disenchanted:

"But where Nielsen could end up being compared with poor August Dvorak and his keyboard is the diminishing return on endless optimization. 66% sounds high for an abandonment rate. Few supermarkets or discount stores suffer anything near that. And yet what Nielsen could be missing is the fact that the web, contrary to his biweekly edicts, is already extremely easy to use. Many e-commerce sites are already about as easy as they're going to get and that's precisely why there are so many abandonned carts: visitors have found it's so easy to play “what if” that they do it all the time, even when they have no intention to buy. There isn't even a manager hanging around to glare at them when they leave without checking out."