Like any true rebel, Scorpio hates being in charge. They worry that something or someone will stop them from getting what they want out of life and being happy.
Taurus values stability and predictability more than anything else. Taurus is most afraid of changes.
Gemini is afraid that people won't understand them. The meaning of this sign rests a lot on being understood, so the thought of it being misread worries them.
Even Cancers who like being alone need to talk to other people. They are afraid that someone they love will leave them. People worry about being left alone a lot.
Leo is most afraid of losing or letting other people (and oneself) down. They'll be damned if they don't get the praise they deserve.
Aquarians care a lot about how they show who they are and what makes them different. Their biggest fear is that they will forget who they are and try to be like other people.
Libras care a lot about both their love relationships and their friendships. Libra's biggest fear is either having their heart broken or breaking the heart of someone else.
More than anything else, Aries is most afraid of being wrong. They don't like the idea of someone telling them what they did wrong or blaming them.