Most of de Bono's writings are about using lateral thinking to solve problems. In his book "Po: Beyond Yes and No" (1973), de Bono describes what he calls an "open block". This is when people ignore certain things that may solve a problem, because they already have an idea of how the problem should be solved. They may therefore not recognise other solutions to the problem. For example, if a person's car breaks down, the open block of being used to being in a car may cause them to wait for a taxi, ignoring buses passing by, without even reading the destinations.