Unintended consequences

Friedrich Engels[edit]
Friedrich Engels touched on the idea of unintended consequences in his discussion of Ludwig Feuerbach:^[4] "The ends of the actions are intended, but the results which actually follow from these actions are not intended; or when they do seem to correspond to the end intended, they ultimately have consequences quite other than those intended."
Robert K. Merton[edit]
Sociologist Robert K. Merton popularised this concept in the twentieth century.^[1][5][6][7]
In "The Unanticipated Consequences of Purposive Social Action" (1936), Merton tried to apply a systematic analysis to the problem of unintended consequences of deliberate acts intended to cause social change. He emphasized that his term purposive action, "[was exclusively] concerned with 'conduct' as distinct from 'behavior.' That is, with action that involves motives and consequently a choice between various alternatives".^[7] Merton's usage included deviations from what Max Weber defined as rational social action: instrumentally rational and value rational.^[8] Merton also stated that "no blanket statement categorically affirming or denying the practical feasibility of all social planning is warranted."^[7]
Everyday usage[edit]
More recently, the law of unintended consequences has come to be used as an adage or idiomatic warning that an intervention in a complex system tends to create unanticipated and often undesirable outcomes.^{[9][10][11][12]}
Akin to Murphy's law, it is commonly used as a wry or humorous warning against the hubristic belief that humans can fully control the world around them, not to presuppose a belief in predestination or a lack or a disbelief in that of free will.
Causes[edit]
Possible causes of unintended consequences include the world's inherent complexity (parts of a system responding to changes in the environment), perverse incentives, human stupidity, self-deception, failure to account for human nature, or other cognitive or emotional biases. As a sub-component of complexity (in the scientific sense), the chaotic nature of the universe—and especially its quality of having small, apparently insignificant changes with far-reaching effects (e.g., the butterfly effect)—applies.
In 1936, Robert K. Merton listed five possible causes of unanticipated consequences:^[13]

• 
  Ignorance, making it impossible to anticipate everything, thereby leading to incomplete analysis.
  
• 
  Errors in analysis of the problem or following habits that worked in the past but may not apply to the current situation.
  
• 
  Immediate interests overriding long-term interests.
  
• 
  Basic values which may require or prohibit certain actions even if the long-term result might be unfavourable (these long-term consequences may eventually cause changes in basic values).
  
• 
  Self-defeating prophecy, or, the fear of some consequence which drives people to find solutions before the problem occurs, thus the non-occurrence of the problem is not anticipated.
  

In addition to Merton's causes, psychologist Stuart Vyse has noted that groupthink, described by Irving Janis, has been blamed for some decisions that result in unintended consequences.^[14]
Types[edit]