There is a popular idea that people are either "left-brained" (scholarly, logical, analytical) or "right-brained" (artistic, creative, emotional). The textbook authors note that these claims are vast oversimplifications based on small nugget of the truth.
The term nugget of the truth denotes a singular element of truth or wisdom within or among a greater story, narrative, speech, or claim, especially when most or all other elements are fictitious or of questionable veracity.