It all starts with sales and marketing cramming every possible feature and half-rumour they heard about competitors' features into a 6 month project deadline. That's a long time, 6 months, no? How hard can it be? Respectfully, it'll be done when it's done.

we are the ones qualified to say what needs to be cut to provide reasonable certainty for the deadline. it is not the job of non-technical stakeholders to mitigate risk in technical projects