The goal of User Experience Design is to enhance customer satisfaction by improving the interaction between the customer and the product. You can follow some best practices that normally lead to a better performance. However, this is not an exact science, and most founders would love to know how their customers are actually interacting with their product.
When the product is web-based, there is a technique called Mouse Tracking that records the mouse movements, clicks, scrolling and keys pressed when they are visiting your site. It's actually like being behind your customers when they are browsing your website.
The results are incredibly positive. I was able to see how dozens of users were interacting with my website from different devices and browsers. For instance, I learned that most of the visitors were interested in my portfolio, and that Android users were not completing the contact form properly.
Mouseflow provides interesting analytics, such as click heatmaps, movement heatmaps and viewport maps (scrolling).