I bet you haven't gone up against a titan running juggernaut with a party crasher +1 that knows what they are doing. The juggernaut shield tanks all damage up to a certain amount (I think 100-200) and any damage that exceeds that limit! So if you were to line up and headshot me with your trusty 1 -k stare, I will still have full health and if I'm too far away for a shot I can dodge away from enemy fire, continue running and after 2 seconds have a full juggernaut shield again and then gun you down as you have now wasted 2 sniper shots and died without claiming a guardian's life.