Saying "I don't know" is arguably more honest, even if it's not useful for budgets or planning.
I completely agree. That's why I chose that example: They're also awful at it, especially these days in North America in particular. But any contractor that tried to put in a bid claiming "it'll be done when it's done and cost what it costs" would not be considered professionally competent enough to award a multi-million dollar budget.
- Create urgency
- Keep scope creep under control
- Prioritize whatever is most valuable and/or can stand on its own
If you just say “I don’t know” and have no target, even if that’s more honest, the project is less likely to ever be shipped at all in any useful form.