[1] By studying experts such as firefighters in their natural environment, he discovered that laboratory models could not adequately describe decision making under time pressure and uncertainty.

He listed his main influences as Hubert Dreyfus, Adriaan de Groot, and Karl Duncker in an October 2013 interview with Bob Morris.

The Arab oil embargo of 1973 meant that pilots needed to do more of their training in simulators, and Klein began his investigations into the way people develop expertise.

The third phase began in 1978 when he founded his own R&D company, Klein Associates, to study a range of topics that are now described as the Naturalistic Decision Making framework.

The ShadowBox Training Method originated from a Master's thesis in 2008, conducted by now-retired fire battalion chief, Neil Hintze.

Klein and others report that ShadowBox training has been employed in the military, law enforcement, healthcare, social services, and petrochemical domains.