Stand-alone risk only considers the risk of holding a single asset and does not take into account total risk. Risk is defined as the probability of an unfavorable event occurring, such as an asset generating lower than expected cash flows. A probability distribution assigns likelihoods to all possible outcomes, such as rates of return, with tighter distributions indicating less uncertainty about outcomes. Portfolio risk analyses the chance that a combination of assets in a portfolio will fail to achieve objectives due to an imbalance of risks within the portfolio.