Once you finished planning out your system the requirements have likely changed. If they didn't you'll find out that you built something different from what the customer wanted once you're finished programming.
I don't think you're necessarily disagreeing with the parent post.
> Ruthless change control is the hard part. That doesn’t mean saying no, it means saying “if you change things, it costs you schedule days”.
Just because software is dominated by soft costs doesn't mean that it's cheap to change requirements. That doesn't mean you can't deviate from your initial spec, it just means you have to charge the customer for changes that they want after you've already started development. Throwing away work just because it's "easy" to change software doesn't magically recover the time and money that you're already spent up to that point.
