What!? Stock Prices Can Decrease?

I went to a seminar about our ESPP today. In the middle, the presenter went over a series of examples to explain how the program would work if the stock price increased or if it decreased. In every example, highlighted at the top in blue was the sentence, "Note: Stock prices can decrease as well as increase." This was a little funny because, 1) Some of the examples depicted the stock price falling, and 2) The presenter would begin presenting his slide, look up and see the blue text, interrupt himself and repeat the blue sentence before continuing with the slide. By the 4th or 5th time this happened, I cracked up. Anyway, seems like investing in almost any ESPP is a good idea. (Note: Please consult an independent financial or tax advisor before taking any action as I am not qualified to give financial advice.)