Sitecore performance in general

After some years of doing a lot of analysis and reviews on Sitecore I would say this my list or reasons when pages perform badly: 
  • Bad code
  • Iterating tons of items.
  • Use of descendants when using axis, xpath or Sitecore Query
  • small use of Sitecore Search
  • No caching configuration
  • cheap hardware
  • bad architecture like only 1 CD
  • missing Loadbalancers