get_the_excerpt() errors where get_the_content() works

I thought get_the_excerpt() would basically be a stripped/filtered get_the_content().

But if I try to swap get_the_excerpt() for get_the_content(), the site crashes. Why doesn’t this work?

function add_to_content( $content ) {
		$got_content = strip_tags( get_the_content() );
		echo "<!-- content: $got_content -->";
	return $content;
}
add_filter( 'the_content', 'add_to_content');