Apart from the fact that few of us are actually investing the money we don't spend on coffee, is the "latte factor" itself actually valid? According to Helaine Olen, author of the well-researched book Pound Foolish: Exposing the Dark Side of the Personal Finance Industry, Bach's theory is based on faulty numbers and incorrect assumptions. She argues that it’s not your Starbucks habit that’s endangering your retirement but rather a financial industry rigged to exploit the average investor, plus larger societal issues like the loss of job security and the unstable housing market. The book is a great (if depressing) read.