A 4-letter domain name has a higher value than a longer name for several reasons. The short domain name will be easier to remember, which is of course very important. The more memorable, the better it is. Shorter domain names are also less prone to typing errors. And a very complicated or long domain makes it harder for people to have it shared on social media, or through word of mouth. And then there is the prestige thing that comes with 3-letter or 4-letter domain names. A web address that is short shows that the site has importance, or that it already exists for quite some time. A short domain name definitely makes a site look more credible.