User:Sam/Portage help/Understanding REQUIRED USE

Example
Here's a typical example of a REQUIRED_USE error/conflict:

Let's break this down a bit. The key part is: The following REQUIRED_USE flag constraints are unsatisfied: wayland? ( gles2 )

i.e. "If the wayland USE flag is enabled for media-libs/libsdl2, you must enable the gles2 flag for it as well."