If you make a Paint or Wordpad window very narrow, the Ribbon and Quick Access Toolbar disappear completely. See the screenshots below.
Imagine such a situation in a small display, where the Ribbon has disappeared in a newly opened window and there is no way to bring it back other than widening the window, which might be difficult due to the constrained width of the display.
EDIT: By design, derived from the Office 2007 Ribbon.
(thanks to user Jaips, for the heads up)
Either disable scaling Ribbonned windows down past a certain point, so the Ribbon is always visible, or add a visual cue that the ribbon is there. Either a version with smaller icons or a dropdown menu.