The success of SEO can be hard to measure because it's measured in metrics. But the ROI of SEO means you'll see more leads, more calls, and more revenue.
Showing ROI means you're thinking like a business owner and not a marketer. Business owners want to make sure every dollar they spend makes a difference, and that it's going to help the business in the long run.
This white paper from Boostability will help you understand what role ROI can play in helping your SEO succeed.