I am so glad I'm not a manager. Managing engineers (particularly those who are ex-quantum mechanics) must be very difficult. When will this task be done? Unless the task is as meaningless as a string change, the honest answer always has a probably in it. And I am particularly difficult to pin down - Heisenberg made a strong impression on me.
But as a product nears completion, you can feel a shift. The tasks are done, and you continue to polish til it is ready to go out the door, but part of the energy starts shifting towards the next release. As work begins in earnest on the next release, it becomes an annoyance to go work on the product that is done in your mind, but not yet in deed.
That's a good thing - we release a more stable product if development actually slows down before delivery, and that's how we build software. But a side effect of that is that when the product actually ships, it's more like a whimper to the engineer. When a product ships now, I sometimes feel like I've missed that moment of birth - it's an oh yeah, it's out the door now, rather than the excitement of being currently focused on that product and being completely overjoyed with its shipment. A release should still end with a bang, not a whimper!