What it is
Lifecycle is everything after the first yes, plus the definitions that let different teams talk about the same customer without meaning different things.
Why it matters
Revenue moves through handoffs, not departments. Most lifecycle failures aren't failures of effort inside a stage; they're failures at the seams between stages, where ownership is ambiguous and each side reasonably assumes the other has it.
Common symptoms
Sales and marketing using the same stage names for different things. Onboarding that varies by whoever runs it. No mechanism for re-engaging closed-lost. Expansion treated as an account manager's personality trait rather than a designed motion.
Related work
The Build Wasn't the Problem. The Gap Was. · Documented ≠ True