Comment by tshaddox

I think the original agile people had the right idea. Do some planning, not too much. Then write some code - but not too much. Then take what you've learned from implementing and replan.

Or if you want another way of thinking about it, code isn't only useful for deployment. Its also a tool you can use during the planning process to learn more about the problem you're trying to solve. When planning, the #1 killer is unknown unknowns. You can often discover a lot of them by building a super simple prototype.