What cause of Google Crawl bots can't find or discover a URL or the URLs?

First and foremost, expected to Google Crawl Bots that content should be discoverable and the existence of content crawled and indexed, after that tries to define the reason and solution for Error pages 404 and 404 page the reasons that because Google Crawl bots can't find or discover a URL or the URLs;

Now, let’s uncover the answer to Why a URL states "Sorry, the page you were looking for in this blog does not exist" (404, Non-Existing Page or Pages)?

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I think my brain just died trying to read that.