Applying the_content filter inside the_content filter causes lots of tears

nested_filters.php

/**
 * I'm going to add some content from one post to
 * the content of another post. Yay for me.
 */
add_filter( 'the_content', 'my_little_content_addition' );
function my_little_content_addition( $content ) {

	if ( is_the_right_content() ) {

		/**
		 * Let's go get another post's content to add
		 * to this post
		 */
		$post = get_post( $my_post_id );

		/**
		 * I want the post to have all the proper HTML
		 * markup, so let's run the_content filter on
		 * it.
		 */
		$content .= apply_filters( 'the_content', $post->the_content );

		/**
		 * You've now made everyone cry by calling
		 * the_content filter form within the_content
		 * filter. In my case, it caused all sorts of
		 * implosions with page builders and WPML.
		 *
		 * If you want to add content formatting
		 * run it through wpautop() instead.
		 *
		 * $content .= wpautop( $post->the_content );
		 */
	}
}