Co-operation? Teamwork? Totally overrated. A YouTuber called Basically Homeless has proved that you can win matches in Rainbow Six Siege all on your own, even in ranked mode. All you have to do is get five PCs with separate Siege accounts all in the one room, get your mouse and keyboard hooked up to a switcher, and then somehow have the dedication to keep playing over the cacophony of five games going on at once. You can see how he managed it in the video above.
Rather than try to switch between characters constantly he tended to play them one by one, treating each death as a respawn. He used the information he gathered about the enemy's location from one life to hit them hard in the next, playing aggressively rather than defending. Sometimes, especially in casual, it went OK!
While I can't imagine anyone else trying this—the nightmare of all those matchmaking errors alone would have made me give up, even if I had five PCs to begin with—it's still an impressive feat and it made for a fun video.