“There are five classes of spies: local, inward, converted, doomed, and surviving spies.”
Five kinds of spy cover different angles; use several so no blind spot remains.
Chapter 13 issues its org chart for intelligence: five classes of spies — local, inward, converted, doomed, and surviving. The taxonomy is not a menu for selection but a portfolio for simultaneous deployment; the following verse says all five must be at work. Each class sees a different slice of reality, and the slices overlap just enough to check each other.
An investor relies on a single brilliant source inside an industry — one person, consistently early, consistently right, for years. The position built on that source grows enormous. Then the source’s blind spot becomes the portfolio’s: the insider’s own company was the exception to every trend he described, and nobody without his vantage — no local, no converted, no public-source "surviving" spy — existed to flag it. One class of spy is one class of error, amplified by trust.
Five sources is not five times the budget — several classes are cheap (locals, public-record survivors) and the portfolio exists to catch each other’s blind spots, not to pile redundancy on the same one. The discipline is coverage: for the decision in front of you, name what you cannot currently see, and check which class of source sees it. Then acquire that class.