The Super Ego is the exact opposite of the Id. It is the part of the mind that is over concerned with morality, and would never react solely based on instinct. The Super Ego is composed of all of the ideals that society has constructed for us, such as the values our parents held or the religion we were raised with.
The Super Ego develops last in our psyche's life. Id is present at birth and is our natural instinct. The Ego is developed in childhood as we learn to distinguish right and wrong.
This morally rooted part of the psyche is obsessed with perfection. The Super Ego doesn't want to do anything against what society as taught it because it would feel overwhelming guilt.
While the Id doesn't care about reality in terms of getting what it wants, the Super Ego doesn't care about reality in terms of morality. It refuses to break any rules. I think of this as letting our culture do the thinking for us.
Super Ego - Listening to every rule that society has taught you and feeling extreme guilt if you disobey one of there rules.