So many times when I’m surfing the internet, perhaps via a Google search, I come across an ugly looking error page because the page used to exist that was indexed by the search engine. Immediately I push the back button and check out the other search results.

Surely it would have been better if they had created a prettier error page within their web-site

template to increase the chances of me staying at their website.

Websites evolve and get re-designed, URL’s change and search engines still keep the older websites URL’s indexed for a while. If a permanent redirect (301) has not been created for an older URL that is indexed in a search engine, you bound to get visitors landing upon an error page. So the choice is yours - Would it not be better create a customised 404 page which includes your branding as a safety net?

… Surely then you would not lose all your visitors trust as if you were sending them to the default ugly version that web servers generate.

I’m sure the web is full of resources on creating prettier customised 404 Error Pages.