Why does the_content not work like others for a set post id?

Here’s something odd, I want to print out a certain post on any page request, if you have a constant $idnumber of your favorite page/message, then add:

$GLOBALS['post'] = get_post( $idnumber );

the_title(); echos that specific page’s title,

get_permalink(); looks ok too,

but the_content() actually ignores the post set, and just prints whatever page was requested, again.

There are many globals that are being set in a loop, not only $post, and you need to set all of them to get exactly the same behavior. To get this it is not enough to set $post but you also need to use setup_postdata