Complex sentence: The most important contribution is Solomon's findings on work motivation and addictive behavior, though it does not fit the "economist's standard model" and how there are growing suspicions that addiction is a much broader phenomenon than first believed.
Split into simpler sentences: The most important contribution is Solomon's findings on work motivation and addictive behavior. Though it does not fit the "economist's standard model" and how there are growing suspicions that addiction is a much broader phenomenon than first believed.