Narrow is a dimension of The Elevate Formula, which is Skill 5 of The 7 Skills to Impress and is discussed in Part 2, Chapter 5 of the book. It is first introduced in Part 1, Chapter 6.
The opposite of Broad in the Elevate Formula. For a High Score Identity person, problems are narrow (limited to one context). For a Low Score Identity person, strengths feel narrow. Reclassifying difficulties as narrow reduces their emotional weight.