Cancer is a very moody sign, and they are prone to overthinking things. Before making any decision, however small, they would thoroughly go through pros and cons arguments, worrying about tiniest of risks their imagination would suggest. It is never black or white for Cancers, and before making a step they most likely would try to envision the worst consequences – just to be on the safe side.
They often turn this critical way of thinking to themselves, picking on past mistakes and what they see as personal drawbacks. This may be ruining practice, and even make Cancers depressed. What they need is a friendly reassurance and a more positive perspective.