404 errors, the dreaded "page not found" message Internet users encounter, are the bane of every good/great webmaster.
404s reveal when there is a problem but the problem may not be their fault. Google's John Mueller recently indicated that most of the 404 error codes that Google identifies are not often webmasters fault, but rather are as a result of others linking incorrectly.
Since 404 errors don't cause ranking issues, they should not really be a top concern. That being said, of course, it is useful to review your analytics account to understand where 404s are resulting/originating from so that they can be me modified in order to improve the digital experience for users.