“Design is not just what it looks like and feels like. Design is how it works.”
Web users do not have time to look for a way how to use your site. The first law of e-commerce says that: if users can not find the product, they will not buy it. If the informations on the website are difficult to read or find, visitors will leave. The result of poor usability is often negative emotion and just because of them visitor will not return. More then 50% of incompleted purchases on webstores are because of bad usability.