Technically, all are true. Sometime the formulation is quite counter intuitive though. The best known exemple is probably the "there is only one room left" mess

Technically, all are true. Sometime the formulation is quite counter intuitive though. The best known exemple is probably the "there is only one room left" message for single room apartments. This has been considered a bug for years. The thing is: any change to the web site, however small, including fixing a bug, must prove conversion-successful in an experiment before going in production. This is both great and dramatic, as you can imagine: great that anyone can change anything as soon as proven successful, but dramatic that often you feel entrenched in local minima. This experiment driven culture is great for the business though. So far. Disclaimer: worked there for a bit.