404 errors aren't inherently bad for SEO when they occur naturally as part of website evolution, but excessive 404s or poor handling can negatively impact user experience and crawl efficiency. A few 404s won't harm your ranking search engines understand that pages sometimes need to be removed. However, numerous 404s indicate poor site maintenance, waste crawl budget on non-existent pages, and frustrate users who encounter dead ends. The real SEO issue arises when valuable pages with existing backlinks or traffic return 404s without redirects. Best practice involves regularly monitoring 404 errors, implementing 301 redirects for important removed pages, creating a helpful custom 404 page with navigation options, and fixing broken internal links promptly.