Avoid anything that is inappropriate for your goals, stage of life, and tolerance for risk.
Some investments are fine in small amounts.
A retiree shouldn't hold a portfolio full of small-cap technology stocks, for example, but buying a few shares for fun would be OK as long as you can afford to lose your stake. Other investments shouldn't be touched with a 10-foot pole. Speculative investments, such as futures, options, and commodities, should be left to professional traders. Investments with the greatest potential return generally have the greatest risk. As the old adage says, if it sounds too good to be true, it probably is.