Greed can cause you to make bad investing decisions. Seeing a popular stock go up in value may make you feel like you are missing out on great riches when you may be buying at the top. Make sure you hit the pause button and research a particular investment before taking the plunge.
Some countries have negative interest rates, which means some savers and bond investors actually pay for the privilege of saving and investing. This could potentially happen in the United States if global trends hold up. What kind of perverse world punishes saving???