I'm in the the game for the whole nine yards. Marketing, requirements, bid, proposal, design, implement, test, deploy...repeat. Sometimes I get lucky and end up recruited into the task after the contract is running. Other times the contract is predicated on access to my skill set. I've endured times when my work is suddenly dictated by a loose cannon in the marketing department. Claims and commitments made in public before checking to see if said items are even possible.
Listen to your customers. They are the ones paying the bills. Scrutinize the rosy projections from the marketing people. Most of it is hot air and wishful thinking. Try to contain your laughter when the Microsoft Project wizards present development schedules and milestones with unwavering authority. Most of them have no idea of the difference between a define process and an empirical process. Software development is the latter.