a bridge too far
An act or plan whose ambition overreaches its capability, resulting in or potentially leading to difficulty or failure. Taken from the 1974 book A Bridge Too Far by Cornelius Ryan, which details the Allies' disastrous attempts to capture German-controlled bridges in the Netherlands during World War II. The multi-million-dollar purchase of the small startup proved a bridge too far for the social media company, as the added revenue couldn't make up for the cost in the end.