Sowell wrote the line in a column about journalism as much as economics. He objected that a Wall Street Journal front-page story on the minimum wage opened with an individual who, he argued, was “wholly atypical” of minimum-wage earners (Sun-Sentinel ↗).
His point was that a legal wage floor does not raise what an inexperienced worker is worth to an employer, so the worker who goes unhired is effectively paid nothing, and loses the experience a first job would bring. Many economists dispute how large that effect is in practice. Either way, the sentence became one of the most-quoted lines in the minimum-wage debate.
They cannot move up the ladder if they can’t get on the ladder.
Where the pull-quote comes from
The pull-quote is from the same 2001 column, two sentences after the famous line. In full it reads: “But they cannot move up the ladder if they can’t get on the ladder.” (Capitalism Magazine reprint ↗).