Adding is favoured over subtracting in problem solving (and software systems)

Consider the 10x10 grids of green and white boxes below. How would you make them symmetrical? Most people would add green boxes to the emptier half of the grid rather than remove them from the fuller half. Even when the latter would have been more efficient. The case, along with a similar problem revolving around the stability of a peculiar lego structure, is reported by an intriguing Nature article on the topic of psychology and human behaviour. »