People. People are the problem. After some years writing about technology and listening to IT experts, one thing is very clear: In nearly all cases, the reason we can't have nice tech things is because of users.
One example is the high-speed rail connection between Singapore and Kuala Lumpur. The air route between the two cities, packed with more than 30,000 flights a year, is already one of the busiest in the world. A fast train would be in heavy use from day one.