As a businessman for more than 20 years, Harlan Steinbaum has made thousands of decisions. However, one call became his career defining moment.Steinbaum, former chairman of Express Scripts, will discuss that moment and his new book based on his experiences, “Tough Calls from the Corner Office” during a Business Forum at 5:30 p.m. April 10 in 126 Social Sciences and Business Building at the University of Missouri–St. Louis.