Reassurance can actually exacerbate anxiety: when you reassure your friend that the worst-case scenario he fears probably won't occur, you inadvertently reinforce his belief that it would be catastrophic if it did. You are tightening the coil of his anxiety, not loosening it. All to often, the Stoics point out, things will not turn out for the best.
The Antidote: Happiness for People Who Can't Stand Positive Thinking (ed. Farrar, Straus and Giroux, 2012) - ISBN: 9781429947602