title: Why do I need FORCE to override a CMake option?
body: <p>I want to override an option, which formely was set to OFF. I am using </p>
  
  <pre><code>SET(USE_OPTION ON CACHE BOOL "Override option" FORCE)
  </code></pre>
  
  <p>Just for my curiosity: Why do I need 'FORCE' (without it, the set() does not work)</p>