Guess the price

I've been reading this book. Fascinating! It's all about what events/numbers/environments influence our (often irrational) decisions. Once upon a time I generated an interesting spreadsheet (described here) which asks you to predict future stock prices (based upon historical stock behaviour). Not possible, right? The past is no indication of the future, right? So what does influence our prediction? Aah, if'n I could only identify investor irrationalizations I'd be a mbillionaire! However, I haven't finished the book, yet. But when I do ...