Good job soldier, you’ve just taken down an entire room full of bad guys. Go on through the door to move on. But what’s this? You need the Blue Keycard! Argh! Time to start backtracking through the level. Oh good, you’ve found it, go on through. Wait, it’s just a small room full of more bad guys! And for what, some bullets? You really need the Yellow Keycard! Argh! Maybe if you hit the “use” button on it enough, it will just open. We’ve all tried it.