I’ve often asked “How do we know when we’re done?” in requirements meetings. It gets people to crystallize what they want and keeps me focused on what’s important.
Any stopping point in software is artificial and arbitrary. There will always be more to do. Features can always be improved. It’s why we all have jobs.
The essence of “when do we stop” is really “what is the minimum result that will satisfy your needs?”. The minimum is faster. Time is money. The minimum is valuable.
The human brain has a problem with this, and folks balk at accepting anything less than complete victory over a problem. However, reality and economics (surprise! they’re joined at the hip) dictate that we focus on the simplest possible solution first. Speed is the key.