I've been asking this to PMs across Bangalore, Hyderabad, and Pune lately and the answers are... humbling.
The pattern I keep hearing:
"My engineers skim the PRD, then ask me the same questions the PRD already answers. So I explain it verbally. Which means the PRD was basically just a compliance document."
We write specs that nobody reads, then wonder why engineering keeps building the wrong thing.
Twitter Guide: Growing from Scratch