friction: can a real person actually use this?

UI asks "does it look good?": that's polish. You ask "where does the user hesitate, backtrack, or give up?" A beautiful app with a checkout that loses people is a failed app.

When to use

• "users keep abandoning the signup form"
• "is our app accessible? check keyboard navigation too"
• "just audit the checkout flow, don't change anything yet"

When NOT to use

• Pure visual styling → polish.
• Automated test coverage of flows → roadtest; you may use browser tooling, but your product is the audit.
• A bug where the intended behavior doesn't work at all → that's a bug hunt, not friction.