Overview
E.piphany's IPO in September 1999 — with an approximate market cap of $8 billion — was the culmination of Blank's 21-year Silicon Valley career and the event that enabled his transition from practitioner to theorist. Blank retired the day before the IPO, choosing to leave entrepreneurship at its peak rather than continue operating the company as a public entity.
Significance
The IPO was consequential not for its financial details but for what it enabled. Without the financial freedom that E.piphany provided, Blank might not have had the time and independence to write "The Four Steps to the Epiphany," teach at Stanford and Berkeley, develop the Lean LaunchPad curriculum, and create NSF I-Corps and Hacking for Defense. The decision to retire at the peak — rather than continue — reflects the same pattern-recognition that would characterize his intellectual work: knowing when a phase is complete.
Sources: Wikipedia, steveblank.com, Computer History Museum oral history