Suppose that 5 years ago you bought stock in a highly regarded company. That same year the company experienced a severe decline in sales due to poor management. The price of the stock dropped drasƟcally and you sold at a substantial loss.
Most investment portfolios have a mix of investments - some of the investments may have high expected returns but with high risk, some may have medium expected returns and medium risk, and some may be low-risk/low-return. (For example, stocks and real estate would be high-risk/high-return whereas cash and CDs (certificates of deposit) would be low-risk/low-return.)
With some types of investment, such as cash and CDs (certificates of deposit), the value of the investment is fixed. However, inflation will cause the purchasing power of this value to decrease.
With other types of investment, such as stocks and real estate, the value is not fixed. It will vary. In the short term it may even fall below the purchase price. However, over the long term, the value of the stocks and real estate should certainly increase by more than the rate of inflation.