Robert King Merton (July 4, 1910 – February 23, 2003) was an American sociologist. He spent most of his career teaching at Columbia University, where he attained the rank of University Professor. In 1994 Merton won the National Medal of Science for his contributions to the field and for having founded the sociology of science. Merton developed notable concepts such as "unintended consequences", the "reference group", and "role strain" but is perhaps best known for having created the terms "role model" and "self-fulfilling prophecy".
Here are some interesting examples of unintended consequences:
Because of the complexity of ecosystems, deliberate changes to an ecosystem or other environmental interventions can have unintended consequences. Sometimes, these effects cause permanent irreversible changes. Examples include:
The introduction of rabbits to Australia by Europeans, which became economically and environmentally damaging, as the rabbits had no natural predators.The draining of American wetlands since colonial times, resulting in flash-flooding and seasonal droughts.The installation of smokestacks to decrease pollution in local areas, resulting in spread of pollution at a higher altitude, and acid rain on an international scale.After about 1900, public demand led the federal government to fight forest fires in the American West, and set aside land as national forests and parks to protect them from fires. This policy led to fewer fires, but led to growth conditions that made what fires did occur much larger and more damaging. Modern research suggests that this policy was misguided, and that a certain level of wildfires is a natural and important part of forest ecology.What do unintended consequences affect our thoughts? Here are a couple of TED Talks that encourage us to be open regardless of what happens:

We're taught to try to live life without regret. But why? Using her own tattoo as an example, Kathryn Schulz makes a powerful and moving case for embracing our regrets.

Brene Brown studies human connection -- our ability to empathize, belong, love. In a poignant, funny talk at TEDxHouston, she shares a deep insight from her research, one that sent her on a personal quest to know herself as well as to understand humanity.