The Stochastic Man by Robert Silverberg

Hugo and Nebula Award Finalist: This tale of an encounter between a probability expert and a psychic is "a treasure" (San Francisco Examiner).
Lew Nichols can predict the future. Not see the future, just make predictions based on research and statistics. Nichols is damn good at it, though, and his accuracy makes him a valuable addition to Paul Quinn's political campaign for New York City Mayor and possibly the White House.
But, when Nichols meets eccentric millionaire Martin Carvajal, predictions suddenly seem petty and flippant. You see, Carvajal can actually see the future-not trends, not options-a signal line of events stretching out ahead. It's a gift Nichols can learn from this "mentor," but at what price? Will knowing the future make the present meaningless?