How often do 4 strokes need to be rebuilt?

I'm curious to know, how frequently is it necessary to rebuild 4-stroke engines? I understand that these engines, being a core component in many automotive and industrial applications, require regular maintenance to ensure optimal performance. However, with the wide variety of usage scenarios and operating conditions, it's not always clear how often a rebuild should be undertaken. Could you elaborate on some general guidelines or best practices for when to consider a rebuild for a 4-stroke engine? Additionally, what factors should one consider in determining the need for a rebuild, and what are the typical symptoms that indicate it may be time for a rebuild?