premise: The "highly confident letter" was a financing tool created by investment bankers at Drexel Burnham Lambert, dominated by Michael Milken, in the 1980s. Its objective was to enable corporate raiders to launch leveraged buyout (LBO) offers without the debt component of their financing package fully in place.
hypothesis: Drexel Burnham Lambert dominated in the 1990s.
reason: It's never mentioned how it performed in the 1990s. It's difficult because the text mentions the 1980s and someone "dominating" in the same sentence which tricked it.