Unfortunately, once your website is up and running, you can't just forget about it. Your website needs regular maintenance!
Every Wednesday, the Drupal Security Team makes security releases of contrib modules. And on the 3rd Wednesday of the month, there is occasionally a security release of Drupal core.
Why these releases need to be implemented immediately?
Because between the time a security release is announced and you make the update, the hackers are vigorously working to exploit as many sites as they can and your site is vulnerable!
As a website owner, you probably have many other important tasks than doing Drupal updates, every Wednesday! (Especially, since any core or module update has the potential to break the site!)
In addition to this, there's other unexpected issues that could come up at any time, for example: