You live by a set of principles and you will not deviate from them without a damn good reason. And sometimes not even then! Not only are your principles likely to get you in trouble, people who know you can use your predictable behaviour against you. (It might be worth noting that even though “Credo” might land you in hot swei, it could go hand-in-hand with the Asset “Good Name” or some such.)
Penalty: As a Minor Trait, pick a credo that will get you into minor trouble. Examples: You will always defend a lady’s honour, you never run from a fight.
As a Major Trait, your credo is a sure fire way to put yourself in danger. Examples: you never leave a man behind; the Captain goes down with the ship; you always protect the weak.