There are other factors that affect the magnitude of risk that are independent of the model. One of them is leverage. Let's say, for simplicity's sake, there is a stock worth $100 and the assumption is that in a week it has 50% chance of becoming $90 and 50% chance of becoming $110. This assumption is your model and your risk is $10.

Now let's say you are bullish on the stock and borrow $400 to buy 5 stocks. In the same model, after gain or loss is realized and $400 is returned to the creditor after one week you are either $50 poorer or $50 richer, your magnitude of risk grew 5-fold by leveraging.