Your mind works slower than most. You find that you have trouble following fast-moving conversations and things like math have you befuddled. While some can rely on their wit to get them out of sticky situations, you aren't so lucky.
In spite of appearances you are not actually unintelligent. Just slow. You find that the world moves far too fast for your liking and you easily get overwhelmed and must take time to sit down and process things. Every time you as a player gets flummoxed mid-sentence or when you come up with an idea, you must pass a check with this trait in order to not simply go silent and forget what you were talking about.
The Keeper may allow you a new check at a later occasion and you may then continue what you were talking about, or present your idea to the rest of the party. You should also role-play your character as this rather slow and dim-witted character. Just remember that you aren't less intelligent than others.