Every website breaks or goes down eventually, even if only for short periods of time. While that’s to be expected, regular users often take this as a sign that your website shouldn’t be trusted, so why not take a bit of extra time in order to build a unique error page to reassure them?
Anything looks better than a default server error message on a white page. A well-designed error page reassures visitors and gives the impression that everything is under control and things will be back to normal soon.
When using WordPress, there are a lot of great plug-ins that can help you set up a custom 404 page with little effort.