Some websites lack a custom 404 ("Page Not Found" error) page, which leaves lost users without any help finding what they were looking for. Not only does this make the website seem broken, but it also seems unprofessional.
We always include a custom 404 page that looks like a regular page on your website, with helpful links to things the visitor might have been looking for, or at least to help them get to a place where they can find what they need.
You can see an example custom 404 page on one of our demo websites here: https://www.lakeridgeinsurance.com/404