He thought that working as the king’s armour-bearer would be a simple profession, because even though he’s basically the king’s bodyguard, most kings don’t fight their own wars. In addition, the enemy would have to get through the entire army before they could get anywhere near the king, so he thought it would be relatively safe.
In the split second that constitutes a flashback, he can see that he was a complete fool for believing such a lie. And there’s never time to regret on a battlefield, when arrows fall like thunder, and the screams of the dying shower the field with blood. He’s beginning to think that his shield wasn’t given to him to protect his body, but rather his eyes. Even so, there’s only so much his shield can cover.
So it’s ironic that he doesn’t die by the enemies’ hands. He dies by the last words and fears of the king, because the moment he realises he’s going to die isn’t the moment he kills himself, nor is it when his king falls on his own sword, but it’s when the king orders him to kill him.