Law of unintended consequences warns that an intervention in a complex system invariably creates unanticipated and often undesirable outcomes.

The consequence can be a positive benefit, called windfall or serendipity. 1/n

Aspirin was introduced as a pain killer. But it was found out that, it has anticoagulant properties, which prevents heart attacks.

In India, there are many cities which has Army Cantonements. 2/n

Large, sprawling areas of land in the heart of the city, with lot of greenery, peaceful atmosphere and walking space around it. Years later, when the city around has become concrete jungles, these cantonment areas are perhaps the only saving grace in an otherwise crowded city 3/n

A classic case was MGR reintroducing (Kamaraj was the brain behind this but MGR took it to a great level) the noon meal scheme in mid 1970s, which led to the birth rate falling rapidly in Tamil Nadu by late 1980's, which was totally unintended. 4/n

More rural parents sent their girl children to school so that they can get the noon meal,and these children attained reproductive age by late 1980s, 5/n