How can I be really good at deductive reasoning like Sherlock Holmes?

What are the best examples of real-world deductive/inductive/abductive reasoning?

• I mean specifically non-mathematical deduction about real world things, Sherlock Holmes style, where somebody followed a logical chain of reasoning to a really compelling conclusion, that nobody guessed before. Bonus points if it led to action that convincingly demonstrated that the reasoning was correct and not a rationalization. Doesn't have to relate to crime. Could be in any domain (business decisions, political decisions...)

• Answer:

  John Snow's work to trace the source of a cholera outbreak in 1854 in Soho, England seems to be a good example of this. Here's a description from the BBC web site (http://www.bbc.co.uk/history/historic_figures/snow_john.shtml): At the time, it was assumed that cholera was airborne. However, Snow did not accept this 'miasma' (bad air) theory, arguing that in fact entered the body through the mouth. He published his ideas in an essay 'On the Mode of Communication of Cholera' in 1849. A few years later, Snow was able to prove his theory in dramatic circumstances. In August 1854, a cholera outbreak occurred in Soho. After careful investigation, including plotting cases of cholera on a map of the area, Snow was able to identify a water pump in Broad (now Broadwick) Street as the source of the disease. He had the handle of the pump removed, and cases of cholera immediately began to diminish. However, Snow's 'germ' theory of disease was not widely accepted until the 1860s. According to the Wikipedia page dedicated to this topic (http://en.wikipedia.org/wiki/1854_Broad_Street_cholera_outbreak), "This discovery came to influence public health and the construction of improved sanitation facilities beginning in the 19th century." I learned of this example in Edward Tufte's book The Visual Display of Quantitative Information. Tufte uses Snow's work to demonstrate the power of information visualization in problem solving. Here's the map Snow used to connect instances of the disease to the location of a water pump.