Fear is a strange thing; it results from doubt, which is of two types: necessary doubt, and unnecessary doubt. Fear results from the latter type of doubt. Unnecessary doubt arises from excessive thinking, and over time fear can turn into a habit. As to what will happen in the future, only the Buddha knows for sure. So if we are always thinking about what might happen in the future, a sense of trepidation naturally arises.
~Khangser Rinpoche ~